Ultimately he claimed to have eight pseudo-patients, but investigation has turned up three, and none match what was described in the paper. (Eg, Rosenhan said it was easy to be admitted, even after showing limited symptoms, but he was actually only admitted after showing extreme symptoms. He said life while admitted was dreadful, but one of the subjects was dropped because he found it peaceful and helpful.)
Occam's razor suggests that there were only 3-4, he lied about their results, and made up the rest. But maybe there were some others, and maybe some of them actually had experiences similar to the paper? But even so, at best, he lied, filtered data, and reported very mixed results as being anything but. More likely....yes, complete horseshit.
There's no real defence of his work possible; at this point it's just speculating over whether it was all lies, or just a misleading mixture of lies and truth, and trying to estimate the damage it did.