I wonder if checking for voice recording devices is now standard procedure in a JC, maybe an active elder can chime in if that's been discussed at elder schools.
My guess is you should have left the laptop at home. By bringing it, that aroused suspicion. And you can take this to the bank: How much you want to bet they checked your phone because they've either used that same tactic themselves or thought about using it. Elder bodies have been known to have their share of conflict between members and I wouldn't put it past them. I'd look for further instruction soon that ALL electronic devices have to be put aside outside of the JC room. Mark my words.