You've got two contextual clues to work with. What's the same about "skateboarding a few days after surgery" and "sipping food through a straw when his mouth was practically bolted shut"? The way in which he did those things tells you the meaning of "trouper."

A trouper is an actor or other entertainer, typically one with long experience

"Trouper" (often "trooper" in American English) in this context is a colloquial way of saying "A person who is reliable and doesn't complain (especially about difficulties)."