Strange... I've been there a fair bit, and they've never touched my hopup nor have I ever seen them touch anybody else's hopup. All the guys that chrony seem to just grab a mag, stick it in, flick the selector to semi, and pull the trigger; absolutely nothing to do with the hopup.
The only absolute reason they would touch the hopup was if your gun was shooting on just the edge of the limit and they wanted to check if the hop was on full (thus cheating the reading), or if it wasn't firing properly. And if either should arise, they should ask you about it first for several different reasons; namely being it's YOUR gun, not theirs and 2, some hopups are RHops (like mine) so you can't go around fiddling around with the hopup too much otherwise you could set it wrong and rip the patch off the barrel when you fire. The staff all seem to be airsofters themselves, so they should know better then to fuss around without permission.
But yeah, I agree with what MaybeStopCalling wrote; it's almost certain it's not done out of malice or ill-intent should it happen. Just keep an eye on them when they chrony (or whenever you hand your rifle off to anybody for that matter) and stop them if you think they're doing something you don't want them to.
Custom VFC M4 - KJW KC02 - KJW Mk1 - TM P226 - KJW M9