Well, of course they mean nothing -- because you know nothing of Ellen's family. Are we not keeping an open mind / thinking outside the box, now?
What they are, is a Lockhart - Rensselaer county connection. And that's at least as plausible a source to look at for your Ellen as an elopement of an unidentiable Ellen Lockhart from Toronto to Troy.
Is this all not a matter of leaving no stone unturned?
This is the only stone I'm seeing to turn, at the moment.
A family of Lockharts in Rensselaer county, where your Ellen Lockhart married.
And compiling all the info one can about them, to see how/whether your Ellen might belong to them.
Either finding a connection in records, or finding descendants of the Rensselaer county Lockharts who know about their ancestry and can confirm or deny a connection.
As I've mentioned, I've spent years doing that with one particular family of mine -- the mysterious name-shifting gr-grfather. I finally, a few years apart, found a descendant of each of his surviving sisters. One had a family tale as nonsensical as the one I had, but different (her ancestor, the sister of mine, was allegedly a "Miss Montmorency from France" when she was in fact a Miss Hill from Cornwall); the other, whose own gr-grfather was even worse than his wife, sister of my gr-grfather, for name-shifting, had a completely fantabulous and false tale of both her ancestor's name and his origin, and had never heard of his wife, her own gr-grmother, my gr-grfather's sister. So finding descendants is not always helpful! But I've just found a mutual descendant of my grx4 grandparents in Nottinghamshire, over on that board, and that may well help me find my missing link between them and me.
A Margaret Lockhart married Samuel Thompson 1852, Second Street Presbyterian Church, Troy, Rensselaer Cty, NY - same church as Ellen's marriage
A Jane Lockhart married Robert Leach 1853, First Presbyterian Church, Lansingburgh, Rensselaer Cty, NY
At the latter church we also have baptisms of the children of a John Lockhart.
Margaret Lockhart 1851 who appeared in the 1860 census in Chicago with Margaret Henderson Lockhart Cloyd was apparently a replacement for the Margaret Lockhart daughter of John and Ellen Lockhart in the 1850 census:
Margaret Henderson Lockhart christened 08 1851
First Presbyterian Church, Lansingburgh, Rensselaer Cty, NY
father John Lockhart
mother Helen (appear as Ellen in census)
film 533484
-- middle name Henderson, clear indication of connection to Margaret Henderson Lockhart Cloyde, of course; John Lockhart, father, would be the son of William Lockhart and Margaret Henderson who married in Paisley in 1811.
Also
Ellen Robina Lockhart, same parents and place, christened 1854
Elizabeth Faulkner Lockhart, same parents and place, 1852
Not exactly the same place as your Ellen's marriage, but same county, same era, and same denomination.

The fact that baptisms for
none of the apparent children of William Lockhart and Margaret Henderson born in Scotland after their 1811 marriage can be found (by me at present) -- edit: that's can
not be found by me -- suggests to me that it's quite possible they had a daughter Ellen/Helen along with Mary, John, Jane?, Robert? ... all of whom appear in censuses in Rensselaer Cty NY. The parish records that would show their children's births just don't seem to be at FS.
And in view of the connection between the mother, Margaret Henderson Lockhart Cloyde, and Robert Lockhart born c1834 Canada, in the 1850 census (son? grandson?), there may even be a Candian connection there after all.
The William Lockhart + Margaret Henderson 1811 marriage is shown at ScotlandsPeople. SP also shows 4 Lockhart births 1811-1835 in Renfrew County to a William and Margaret (5 births in total using spelling Loc*rt). I can't see any more detail, but guessing finds Mary, Jean and John. Those births do
not appear to be shown at FS. I couldn't guess who the fourth birth was, but it was apparently not *len or el*.
Process of elimination ... dog with bone ... the fourth child's name began with A...r...c -- ?? Oh of course, Archibald. But Jean was spelled Lochhart, so that leaves one. And that one didn't seem to start with any of the 26 letters of the alphabet. What am I doing wrong? It would take 1 credit to see the 5 Loc*rt births 1811-1835 to William and Margaret!
Argh, it was a third "J". Janet.
I wonder whether the middle initial H for Robert H Lockhart c1834 Canada was for Henderson.
(I need to clear my eyes. I just read the name of the mother of a Monroe Henderson Lockhart at FS as Fattie May Roy. Mattie Fay ...)
(I've tidied and added a bit to this message too.)
And I have to ask one more thing: does the marriage record for Ellen Lockhart and James Clezie definitely say that she was unmarried at the time of that marriage?
She was about 24 at the time, if born 1816. William Lockhart and Margaret Henderson married in 1811. It's conceivable that they had a son, name unknown, born 1811-1818-ish, who married an Ellen and died, making Ellen a Lockhart by marriage and daughter-in-law of Margaret Henderson Lockhart Cloyde. Just a thought.