why did he let me hit him?

so i sparred with the head mt guy and for the first 30 seconds or so he was just barely moving but of course bobbing around with his hands up of course. he straight up let me punch him without him defending himself and when he was doing this it was sort of intimidating.

i punched him in the face like five times and he was not fazed one bit. then of course after that when he decided to fight back he did a combo and got me on my jaw and temple really good and then the round ended. good enough to where i felt it for days.

why did he let me attack him like that?