The thing with game development is you don't have 300~ people working on a game all at the same time, from start to finish.
Different phases of development require more/less people than other phases of development.
I would assume Remedy is allocating staff to a project in a dynamic per-needs basis... So if a project needs 150~ staff for a few months, they allocate that... Then after that need has stopped, shift them to another project.
It's ensuring everyone is kept busy every day... Rather than forcing the hire/fire cycle that oft-plagues game development.
Although, they will probably need to do some more hires...
--::{PC Gaming Master Race}::--