It's not outrageous for teachers to suspect botulism; after all, there were some high-profile cases of infected cans exploding a few years back. It's just funny. HA HA THE CAN FARTED! It had to be said.
Actually, exploding containers are not unheard-of in food service, particularly in restaurants that require staff to "marry" ketchups and other condiments at the end of the day, filling up jars to put back on tables. If a ketchup bottle gets refilled over and over again for years, the stuff at the bottom can ferment and bubble, until finally, kablooey.
Image source: CHOW.com