Later, with reflection, the aggression makes sense. Cultists bring nothing but trouble.

For now, John is still offended and irritated, but... Trying. Negotiation seems to be working, even if he wants nothing more than to exit this conversation and the area.

Arthur would probably do something stupid like offering the truth to this clearly unhinged man.

"... We were infiltrating a cult before waking up here." John says, leaving in a grain of truth despite himself.

This guy seems to have a problem with cults, after all. Maybe the implication of subterfuge will get him to back the fuck off.