So the guy was angry at himself for losing, punched a wall and teared up a bit? I'm kinda embarassed to say it now but I used to do that too when I was playing Varsity tennis in high school and I lost a big game. Doesn't mean I did roids. On top of that, the guy does competitive MMA fighting which is the most aggressive sport in existence. It would tend to attract aggressive personalities don't you think?
I'm not saying steroids don't cause over-aggresiveness but the people who go into "roid-rage" are ones that are probably already fairly near the tipping point to begin with... And now they have the muscle to back it up.
I would say football attracts more aggressive people then MMA, if you look at the champions of MMA, they are very calm, cool and collected (GSP, JJ, JDS, Andy, Frankie etc). It's more of a stereotype that if you are involved in MMA you are some jerk that likes to fight.
Honestly, I'm not going to do the research, but I'm confident that higher testorine levels lead to increased aggression in any type of creature.
But you take someone who's already aggressive then throw in the roids, it's easy to see why they blow up. I'm not even going to explain why your anology about blowing up at tennis vs. the clip I provided is bad.