Help. My Egg went Fukushima

Hello,
I'm a newby. 
I picked up a large BGE 3 weeks ago.
Sometimes I get the temp right and sometimes I don't.   I installed a BBQ Guru CyberQ for long cooks.
I had it pretty well dialed in on a simple pork loin grill so I tried a longer cook.  One rack of b-backs and a small pork butt.  After getting the egg to 225deg I inserted a probe into each meat and placed them on the grill rack (Placesetter Legs Up).  

Well the probe in the ribs was stupid (I think) because the meat is thin.  The CyberQ started alarming on the ribs.  Stupidly, I ignored the alarms on my iPhone.  I assumed they were just for the ribs, and didn't pay close attention to what was happening to the overall temp of the egg.  I deserve your LOL's.

2 hours later I go to wrap the ribs and I see that the egg is at 500+deg.  $50 worth of meat is toast. 

Here is what I "think" happened.  The chunks of peach wood I used were too large. (the size of a baseball)  Once they lit up there was no way to control the temp.  It became a runaway reactor.

Is this correct?
What size should my wood chances be?

Many thanks

Luke