An innocent person who hears #2 may reason that the police are faking evidence, they'd better give a fake confession because otherwise the police will just use the faked evidence in court. He may not be up to date on the laws about exactly at what steps in the process the police are allowed to use the fake evidence.

Alternatively, he might think that his friend actually implicated him and that he has the choice of saying nothing and being convicted because of that, or confessing to a lesser charge.

Alternately, he might just think that police who'd fake evidence are corrupt, and that corrupt police could do a lot worse, like fake evidence against his whole family or just shoot him, so he'd better confess just to come out of this alive.