It isn't a joke. With memory safety bugs the value of an object can unexpectedly be any bit pattern. That breaks the assumptions of basically every language and leads to pretty much anything happening.
If you have an array of objects of the same type and you just pick the wrong one, then the data still has to be a valid bit pattern. Yes it might still be a security bug, but it's much less likely because you aren't completely subverting the language.
Surely you don't think all bugs are the same because they are all bugs?
It takes a lot more for a program to be correct than having valid bit patterns.
To begin with, the whole point of classes is to maintain invariants. Guaranteeing that a location in memory matches the valid bit patterns of its members is far from sufficient.
