Hang on - got it. You mean:
They're his signings in that, from a list of a few players, he's gone 'Ok, that one'.
Anyway, yes, that's what a "manager's signings" means - at any club.
The usual exceptions are when the owner insists on a particular signing, or a director of football makes the...
If Oscar approves them - as I'm sure he has/would - they're his signings, regardless of who found/recommended them.
I very much doubt Alex Ferguson found m/any players himself. That's what scouts are for.