How do riots and death threats equate to suicide bombing?
Here's a quickie paragraph for you.

MAIDUGURI, Nigeria (AP) - Nigerian Muslims protesting caricatures of the Prophet Muhammad attacked Christians and burned churches on Saturday, killing at least 15 people in the deadliest confrontation yet in the whirlwind of Muslim anger over the drawings.

And here's the answer to your question: probably because they both kill people that had nothing whatsoever to do with the situation. How do riots and murders -not- equate to suicide bombing?