I don't how this could have possibly happened because I know he had a surge protector and aren't those things supposed to trip when there's too much voltage going through them?
Sorry, but that just isn't true. It may have just been a freak incident, but more likely your friend probably pulled too much current through too thin of wire gauge. Circuit breakers are meant to protect the wire, not the devices. You can pump 16A through 24 gauge wire and it wont ever trip a 20A breaker, but your wire gets too hot, the sleeve melts, and now you have a wire that is 110+ degrees Celsius exposed.
Do yourself a favor and get a Kill-a-Watt meter. It will give you a little piece of mind. Find out what other outlets are controlled by the breaker your rigs are on, and then add up the total amperage of all devices on that circuit, including your rigs. You should be at no more than 80% of the breakers capacity. If you did any DIY wiring, make sure you used the proper gauge wire for the current its carrying. Over gauge the wire if you are extra worried. Also, make sure your PSU power cables are gauged heavy enough for the current they pull. Lastly, make sure your surge protector is rated to at least 15A (most are).
With the rig you are describing you have, I highly doubt you have anything to worry about.