Killers Disconnecting on Console

Why is the killer able to disconnect in a way that ensures the survivors do not recieve any of their points or pip up? Just finished a match with a camping tunneling leather face.

A survivor disconnected in the first 5 minutes of the match. We end up completing the gens with just 3 survivors and the killer disconnects.

He claims "my friend sent an invite and you guys already won." I doubt that considering he went out of his way to DC in a way that negates our performance.

If behavior is unable to remedy this problem then at the very least a time band of a minimum of 15 minutes should be put in place for those who DC.