Are you sure that all they smoked was pot? Perhaps this place is more sinister. Could all the stains and films and resins on the walls be from a Meth lab? People can use tin foil or a clear glass pipe to smoke meth. Though I think meth users would be more carefull about not losing any and wouldn't leave a bong behind. (Some even recapture the drug from their own pee.)

If the place smelled like a cat box, I would consider the possibiltiy. If it was it would be a danger to you.

The meat in the fridge sounds very sinister. Do they eat roadkill?