Commendable action indeed. Thank goodness.
However, the good guy needs more firearm training.
After watching the video, here are a couple examples:
1.) Don't close the distance with your firearm against a knife attacker. Keep distance! You have the advantage, knifer doesn't. He was arm's length away, which is a no-no; it plays to the knifer's advantage. Knifer is an established threat, so one lunge is all it takes. Also, there were many people joining in to swarm. If a lunge were to happen, friendly fire crossfire increases.
2.) He held his pistol in one of the worst ways: sideways with the other hand over the slider. Bad form! He shoots with a poor grip which will result in an inaccurate shot. Poor grip also increases the chance of dropping it and will injure his left hand in the process.
There's zero reason to hold the firearm like that.
I highly recommend people who own firearms to take training courses. Your life and others might depend on it!