Its called called ostracitoxin. Boxfish have the ability to do this yeah, but IME it is VERY rare. They do however feel threatened with their own kind. But I had a boxfish that was fighting Velvet for almost three months and when died still did not release the toxin and wipe out everyone else.
Also I have seen many LFS, put these fish in with aggressive tangs and triggers, get nipped at and still not release toxin. In all the time or known others to have them I have never had one release toxin. But its a good thing to know that its always possible it could happen. keeps you scared and leaves all the cool boxfish for us.
