Great technique can usually trump any size advantage. Granted this was a street fight but still, the way the little guy countered his opponent’s size advantage is a lesson for the ages. There’s a reason why the under-sized Gracies dominated the sport against bigger and stronger opponents back in the early days of mixed martial arts. Watching how this little guy pulled out a rear naked choke in street fight is prime evidence that mixed martial art techniques can be used in various combat settings, not just inside a ring.
Street fights are messy and potentially dangerous affairs. The risk of significant damage to both participants and the potential for things to escalate beyond unarmed one-on-one combat is great. This is the prime reason why street fights should be avoided as much as possible. That being said, performing a high-level MMA technique in such a setting is still an admirable achievement.