Not only are you not weird - you are absolutely correct. It is incredibly inappropriate for Robert to have his child sleeping with someone who is essentially a stranger to him. Even if nothing ever happened, it models really, really bad boundaries to the little boy as he grows up.
If, god forbid, child services ever got involved in their family somehow, they could actually find that this living situation is unacceptable and force Robert to find a separate sleeping situation for his son. In fact, in evaluating a foster home, most child protection agencies won't accept sleeping on the couch