dang that's clean and nice~
the breakdown my opinion: if that one purplest rock is true live plus the sand being wetpack, that is the source of the bac
*the other rocks may well be live, I could store rocks in a dark vat for 5 mos getting bac ready, take them out for sale as live rock, they'd be white like those but still filters.
what live animals are attached in there? true coralline is the best. it takes months to adhere, bac adhere in days / weeks. if the rocks came from a live rock vat with starfish, pods crawling around, some of the rocks have algae on them, that's all visually-verified ready rock. the bacteria don't die when they come home to your tank, and if they were producing ammonia v scrubbing it your testing would get purple, fast. pictures tell more about ammonia tracing than testing does unless seneye is being used.
next up is little white round fanworms, months to accrete onto the rock.
then sponges and motile pods, little waivers of algae or strands of various organisms associated with being underwater stand out. its fun to try and locate and prove the existence of bacteria without any testing whatsoever, those types of inclusions seal the deal can't wait to know if macro pics or inspection shows live animals.
that top purple rock could also be liferock previously dry, and the rest of the rock dry, that leaves room for the counter claim to state its not ready yet. so we have to hunt for tiny associated proofs to seal it up...