The Tew-Tew Marriage

A number of years ago while searching for a different Tew marriage, I found in the Ontario indexes an 1875 marriage in Hamilton, Ontario where both parties had the surname Tew. Or at least that is how it appeared in the index.

At first I thought that perhaps it was an error with the index, that the indexer accidentally put one surname down for both the bride and the groom. But when I got the microfilm reel and found the actual marriage registration record (shown below) I discovered that there was in fact, no indexing error - both the bride and groom had the last name Tew: Martha Tew and John Armstrong Tew.

My next thought that perhaps there was a remarriage - i.e. perhaps the bride's first husband died, and she was marrying her brother-in-law, which wasn't unheard of at the time. But it appears that Martha Tew hadn't been married before and Tew was her maiden name.

So, next I figured perhaps they were cousins, so I started researching their respective families to see if they had a common ancestor. Now here's the weird thing: John Armstrong Tew (my line) comes from Ireland and Martha Tew's line comes from England.

So, what I can conclude from this, is that either:
a) They are distant cousins, due to a connection that I haven't found yet
b) As a strange coincidence, two individuals both having the same uncommon surname happened to meet and get married.

Can anyone else offer another explanation?