Dr. Lecter
Contributor
The diver shouldn't panic if somebody taps on the shoulder as it could be just another diver desperately needing air. Same if the diver sees somebody swimming from the wreck, as it could be just a big shark, turtle, spooked grouper or stingray. If the diver is thinking about panicking in these situation, then maybe he/she shouldn't be diving at all or maybe going through some training. The panic kills divers not the free divers having fun.
To be clear, the concern isn't so much that the gas-carrying diver will panic, but that they will react in a way that could injure or kill the guy who's on a single breath at 100'. Unlike pretty much anything else swimming in the ocean, an unknown human reaching for you with unclear intentions presents a threat, and people react to threats in different ways.