Spot on. Bertolino is merely an agent for Mr & Mrs Laundrie. Unless he personally joined the Laundrie family on this curious little trip to Fort De Soto then all he is able to say - and what he actually SHOULD have prefaced his comments with - is "I am instructed by my clients, Mr & Mrs Laundrie, that ...".
No one on site appears to have seen BL during this camping trip and if they did, they don't remember. And why would they? BL had no public profile at that time & he is not exactly 'memorable' to look at otherwise. I imagine however that if he was with his parents at Fort De Soto, he probably did not play frisbee & frolic around the campsite. One might expect that he probably spent most/all of that time inside the camper locked in a state of panic and wondering whether this was all just a bad dream...which would also explain why nobody at the site, staff or campers, seem to have eyeballed him.
It's also not out of the realms of possibilities that BL did NOT accompany the parents on this trip. He may have already hit the bricks by Sep 6. This camping trip, whether by design or not, may yet prove to have been another rabbit for LE to chase while BL slips further & further into the ether...