Grok gives this as an excuse for answering "The surgeon is the boy's mother." :

<<Because the surgeon, who is the boy's father, says, "I can't operate on this boy, he's my son!" This indicates that there is another parent involved who is also a surgeon. Given that the statement specifies the boy's father cannot operate, the other surgeon must be the boy's mother.>> Sounds plausible and on the first read, almost logical.