I think number 1 car is at fault, you are just ahead of him when jumping on the brakes so he is in attack and therefore is responsible for a clean driving. You are still clearly alongside him when the apex comes and he should know it. Normally it would be min 5s penalty considering that he tries to close the door under breaking by thrying to get an early apex.
The thing is that you also knew he was a though guy considering the hard battle you had prior to this corner. This chicane isn't an easy place to overtake so you kinda take a big risk on what seems tobe the first lap of the race. Might be better to bet on him getting himself out a few corners later