Part of it is going for a play and not realizing their whole team is there.
Probably just this honestly. He tries to set up a flank (smart play), but fails to realize that should the enemy team retract and your team hasn't engage, he'll just straight up die. So to you, it might look like a stupid play despite him potentially setting up a play that gives you all your best chance at winning or for a pick. However , he assumes you all would engage or go in just because he used R to flank. That clearly was not the case.
As someone who plays a lot of TF, I've personally done that and (probably single-handedly) lost matches before. Your team hates you and they sometimes think you're trolling. Despite that, I've also hard carried with TF and set up some amazing plays that won us the game. Sometimes I think its my team's fault for not following me up- however we know that's a logical fallacy because its not their duty to back me up when I go in deep. The safer plays are generally the more intelligent ones when you're behind, as looking for picks could cause tilt, flame wars, or just end the game.
My point is here that- and I promise you this- you've probably had games where you picked a bad fight and your team was just like ?????. It's usually just communication or believing your team will followup and they don't. Unfortunately TF is kind of a do or die pick. If he's ahead, he can ult in and pressure the map. If he's behind, his ults useless- really his only option is to look for plays or use it for vision/cross map wave clear.