we have a cycled tank

it cannot be a wrong call. to be mega technical you need to identify actual inclusions on your rock to seal the deal...but imagine how much bad luck you'd have to endure to show up to lfs, they have all that machinery running but only for rocks formerly dry just added a day prior (so they wouldnt be ready) and in the end they sell something fake labeled as live.
I cannot imagine such a series of events lol based on known history alone
but to seal the deal, its a single fanworm attached and sticking out. a living accreted animal takes orders longer to adhere than filtration bac, when underwater.
or real coralline, coralline seals the deal. anything with coralline on it is cycled. coralline takes months to plate onto
or algae of any time/ little corals that might be attached. something scummy and slimy feeling, all that is proof of nitrifying bacteria though we cannot see those without specialized gear. we can infer them via known order of ops for reef building organisms and associates.
do you have any growths of life at all on your rocks