Here is a possible answer to the riddle.
The Alexander Smith, described above as a carter and the possible father of Alexander Smith (Easson) born 1862. we have this 1881 census,
19 Butcher Row, Dundee, Forfar.
Alexander Smith, Head Carter, M. age 54 years, M. born Dundee, Forfar,
Janet Smith, Wife, M. age 60 years, F. born Scone, Perth,
Isabella Smith, Daur, Jute Millworker, U. age 13 years, F. born Dundee, Forfar,
Euphemia Clark, G Daur, Jute Millworker, age 10 years, F. born St. Cyrus, Fife.
Now there are no births for a Isabella Smith, of that age to parents Alexander Smith, and a Janet, in the area concerned, however there is a birth of a Isabella Rutherford, 2/July, 1867. to a mother Janet Rutherford, Dundee, Angus.
Then on the 24 Aug/1872. Dundee, Angus, there is a marriage of a Alexander Smith, to a Janet Rutherford.
Its quite possible the Alexander Smith, born 1862. to Margaret Easton, who died 1864. might have got his mothers surname mixed up on his marriage certificate, after all he was only a small child when she died.
Very close to the above address 13 Fish Street, 1881 census we have,
Alex Smith, Lodger Coal Carter, U. age 18 years born Dundee, Forfar.
Just a Thought,
Regards,
Jonn.