It’s pretty easy when you are thinking in English. I’m from Slovakia and in our language we have different forms of words for male and female professions. Chirurg for male surgeon and chirurgi?ka for female. So I subconsciously translated it in male form.
BTW We have also two forms of surnames, so mother and son have slightly different names… tricky language. :D

I said his “father” was his priest. :-/

Sad, I’m sure I’ve heard this one before. lol

There are any number of options here limited only by the legal definition of “son.” For example, the surgeon could be the boy’s step-father, legal guardian, etc.

The surgeon can be the boy’s father too, like in “gay”

A surgeon can also be a woman, therefore the surgeon must be his mother.