What would cause a perforated colon if not diverticulitis?

Several causes: Cancer, stercoral ulcer (hard stool which erodes through the bowel, obstruction (a blocked colon will usually perforate at the right side [cecum], )trauma, ulcerative colitis, and toxic megacolon associated with clostridia difficile infection, are all possible causes of colon perforation.

Many things: Poor blood flow, foreign objects, ulcers, severe constipation (stercoral ulcers), .... Many many things.