I don’t think anyone has posted that you did something wrong. Your initial post re Harriet was on another thread which must have had a surname connection or something.
It often happens when people like yourself are searching and spot a name.
The moderators then make a new thread just so that your query can be dealt with as best we can.
I have been confused because nowhere can I see John and Harriet in 1851 and more specifically a reference to ‘Bohola’.
I have seen a public tree which gives a birthplace of ‘Tombohola’ but no supporting evidence.
As you say, there are several Duffys living in the same area in Hull. They may be related.
I have tried to follow some family members to see if they give a birthplace.
The only one I can see is Patrick b 1845 who marries Hannah (I think it was) and he shows Aghamore. Do you know if that is the same Patrick as yours?
Some parishes in Mayo do have registers going back to 1830s etc but Bohola and Aghamore do not.
Unfortunately, as John and Harriet did not have any children in England, to check her maiden name and as Duffy is a common name it is difficult to find records to help your search.