I know some of Forrest's training partners, and from everything I know about him through them, he is a great guy, very down to earth, funny, but a very sore loser, and he thought that he'd lost the fight, a fight into which he'd put a lot of heart, and that he also wasn't happy with his performance.
Re. Sonnen's spinning bak fist. He tripped because 1) he was leaning forward too much without his feet under him, something aggressive and untalented strikers tend to do, and 2) He actually got his right foot caught but Anderson Silva's left. (Always watch the feet, that's where most of the fight takes place) That's the foot that needs to plant directly after a spinning back fist. He caught it before his momentum stopped, and it landed him on his ass. This is why any good striking coach will plant into your head. Keep your center of gravity under control. Some guys who are super orthodox boxing coaches will tell you to never cross your feet, never bring your feet together, etc... but that's BS, especially in MMA, where the distancing is completely different. The important thing is to not lose control of your momentum. Or else you'll end up like Chuck Liddell in his fight with Franklin - KO'ed throwing yourself into a punch. Watch the footwork of say, Junior dos Santos, who is a large ass man who can get out of the way of counterpunches very quickly. His feet come together all of the time. He will actually throw, draw his lead leg back, then reposition his back leg. This would give a boxing coach a conniption, but It's a useful way of moving out of range when you are not just avoiding punches, but also kicks and takedowns.
I'm going to get on my soapbox for a bit. MMA is not just a combination of wrestling, BJJ, Thai boxing, and boxing. It can incorporate anything that will get the job done. Karate, Sumo, Kung Fu, whatever. It surprises and dismays me when fans, and even top guys, say "this will never work". MMA was built on trying new things. In UFC 1, now one knew wtf Royce was doing. Until Anderson Silva and Lyoto Machida KO'ed 2 top fighters with front snap kicks, everyone was dismissing them. Stupid. There should be more thinking, and less hewing to the Orthodoxy, which was what MMA was against to begin with.