If it's what he wants to do and it's legal, I have no problem with it.
If he'd have kept it and ate it, that would have been a sure death for the fish. At least the fish had a chance for survival this way.
The fish may have died, but we don't know that for sure, and anyway, it IS just a fish.
Lots of ego in fly fishing. This is pretty minor stuff.
But in answer to your question, if fly fishing is a sport(and I'd argue that one), and you do it according to the rules, then why can't it have been both?
Buddy
It Just Doesn't Matter....