That bulkhead is not thin material, is very strong...and was blown backwards and apart from something that occured in the cabin.
Like what?
Just look at the most recent pics of that bulkhead. Thin is a relative term. it's peeled back like a tin can.
At altitude it must withstand something like 10 tons or more of pressure. Seconds from touchdown, the internal and external pressures had to be equal.
So, like what? An out-of-control food/drink service cart just prior to landing? What?
Ten tons or... ?