He can say whatever he wants. People, and simulacrums of people, lie. A rogue robot who found a way to emulate human readings? Or a designer (Hopkins) who introduced a new breed of synthetics indistinguishable from biological humans to put chaos into the system? Is that really out of the question?It's not just that the MiB said several times that he'd been coming to the park for 30 years; it's also the fact that the guns didn't harm him.
Granted, the writers have probably and sincerely flipped the Gunslinger story from the original Westworld. I'm just making suppositions for fun.