At a company that size there doesn't actually have to be much more to it than what they say. Project A might have too many developers and not enough QA, project B might be short developers and too much QA. Project A gets dev positions cut and project B gets QA positions cut, but they're still hiring for the open slots in both cases.

At a small company, it's fairly trivial to just move people from A to B etc. But when you're steering a ship with thousands of employees it's not worth it.