These fighters hold in a whole lot of emotion, stress, nerves, mental fatigue, and endless hours of blood, sweat, and tears to fight on the main stage. They are celebrating winning via injury, they are just reacting in the moment at the the release of all of the above and tension.
If you have ever competed, especially in front of a large audience, you would have a better understanding of just how some people are when they release it.
The adrenaline rush alone can be overwhelming. Some people will shake uncontrollably as the tension is released.
The first few minutes at the end of a fight is not the time to judge a person.