Stupid.

If you're going to break a law, don't tell anybody.  Especially if you're breaking that law to try to be a defensive bulwark for the helpless. 

Stupid fucker told his students he was carrying.  Yes, it made them feel safer.  However, word does, and did, get out.  Even worse, he did it in the People's Democratic Republic of California, where private property isn't private property if it's your car in a school parking lot with a gun locked inside it.