I wouldn't fault anyone for shoving the river but I think it's important to remember that river raises with less than near-nut hands are rare. Especially for a 65/5 type player. I'd be very, very surprised if this was EVER a naked ace or even two pair. And far from every player would even raise a hand like T9 on this river.
On a related note, follow me on this piece of logic: Slowplaying is a "trick." Someone who slowplays isn't a complete beginner because absolute beginners don't realize that it's even an option. They don't think one street ahead, "if I just call now, he will probably bet again on the river and I can raise him then." This guy apparently did or he rivered something that improved his hand enough that he felt comfortable raising. That brings me back to the point that very few people will look at AJ on this river and think it's worthy of raising, so if the river improved him it could maybe maybe be AQ. But again, raising AQ on the river isn't really something 65/5 players do generally speaking.
So, someone who slowplays can think one street ahead, at least occasionally. So unless he's a complete peanut who thinks that AQ is good enough to raise on the river, he looked at the turn and decided his raise could wait. Would he wait with T9? With a flushdraw and a straight draw on the table? Possibly. But I'd argue that it's a little bit rare for that to happen.
But, like I said, I wouldn't fault anyone for shoving, but just remember that river raises from fish generally mean the nuts or very close to it.