Watching the clip a few times it seems that it one sections got lucky with a grenade. The rest was simply due to an overwhelming amount of manpower being thrown against a smaller force.
It could have easily failed but RNG won out and the UKF player got away with it.
Tbh the same thing would have happened with the same number of volks vs 2 vickers etc.
The UKF player would have been better off using the smoke barrage though tbf.
