You are saying they did not teach him TWC? Or are you saying when he fights he only used BJJ and did nothing but BJJ?
Noone wins a fight without being what they are, and what they are is usually a combination of all their training. They are fighters. Not TWC or BJJ fighters but simply fighters.
If you've learned more than one striking method, you can of course choose to use only one or the other.
It was said he trained kickboxing for competition. Based on the information given and what has been shown, the striking method used was non-TWC. So, it appears he used a combination of kickboxing and BJJ, unless something more can be shown.
So, all I'm saying is the credit for which style was used to win the fight should go mostly to BJJ, for the takedown, groundwork, and RNC that finished it.