A potential tender offer isn't always non-public though. The ones which are non-public are presumably less likely to be discussed somewhere as public as over a bathroom stall. If you as a random Joe unaffiliated with the companies in question don't know it's material non-public information then you can trade on it.

The other facts might matter, like if you bragged to somebody about the non-public information you overheard (or, as in this case, where you were a member of the company in question), but it wouldn't be a slam-dunk case if the only facts were trading on bathroom stall intel.