I didn't see Brock being a baby in that video at all.
For one, he was right about Mazz not haivng Mir release the leg soon enough. I remember watching the fight and I was like, "WTF is Mazz doing? Or rather, NOT doing?" With the way Mir grabs a limb, I was wondering how long Brock would be out due to a leg injury, luckily, nothing came of it.
Two, Brock wasn't being a sore loser in the least, he admitted that Mir got the leg, he was simply upset that he lost. When you're as competitive as he is, especially only losing 5 out of 111 wrestling matches in college, that dude FEARS losing like we couldn't even begin to understand, it's no wonder he's training so hard to stay on top.