The male koala wanted to mate with Toby's mother. If she did and conceived a joey (initially the size of a jellybean in her pouch) that would be incentive to abandon Toby. That's why males try to separate females from their joeys.
However, females do have some leverage in the mating process. I saw a little video on a male koala very gingerly tiptoeing toward a female koala who was trying to drive him away with these rather horrible koala screeches. She may have had a tiny (jellybean-sized) just-conceived joey in her pouch.
Male koalas also screech when they feel under threat. These screeches are sometimes recorded and it is really incongruous to hear such fluffy teddy-bear types making that kind of racket. But I guess that noise help koalas defend themselves.