Mysterious name change?

I had spotted a likely marriage of one of husband's Flemings, Janet b 1840 to James Smith coal miner in 1860 in Patna but could find no further trace of them.
I thought no more about it until I had an email suggesting that Janet was the wife of James Scullion. Further investigation revealed that they were recorded in the 1861 census as Scullion. I got the marriage certificate from scotlandspeople for more information. It was the right Janet Fleming and his parents were Hugh Smith, seaman and Sarah Mclean.
Ancestry research goes so much better when there are more than one of you researching and coming at it from different angles. The Scullions were from Ireland. We locate the family in the 1851 census at the Netherton Coal works in East Kilpatrick, Dunbartonshire. Sarah Scullion is a widow, a house servant, born Ireland 1811. Three children are with her John Scullion 20 a coal miner, Mary Ann Scullion 18 a dressmaker and the aforementioned James Scullion all born Ireland.
In the 1861 census James and wife Janet (Fleming) along with baby Elizabeth (named after Janet's mother following Scottish naming patterns) are at Gartnavel Farm in the parish of Govan in Glasgow and with them is his mother Sarah aged 50 formerly a servant. He is still a coal miner.
So why was he calling himself Smith when he got married? I and the other researcher exchanged emails with all sorts of suggestions and I posted a query on the talkingscot forum. At last, an experienced researcher came up with what I am satisfied with is the solution.
Irish James, the nervous groom, would be asked his name. "Smith" was how the registrar heard it. When asked father's name he answered Hugh. Since James was illiterate (from his x mark on the marriage certificate) and Janet was barely literate (from her handwriting) they did not know that the wrong name had been recorded. Sometimes you just have to picture the situation!
Baby Elizabeth, born in December 1860, is registered by her mother as Elizabeth Fleming Smith. I can only presume that Janet had the marriage certificate with her to prove the baby was legitimate. The next child John born 1863 is registered Scullion with no mention of Smith. The only other mention of Smith is on wife Janet's death certificate where Smith is middle name of her husband, informant their son John.
I have emailed scotlandspeople to ask how the Scullions could have sorted this out, if there is a record of it.
As for James's father Hugh who was deceased by 1851, he is variously recorded as a seaman, a farm servant and a seaman in the US navy! Another mystery to be solved!