It was a simple over-boost. It sounds like you attempted to go WOT in too high of a gear (5th?) where you had a high load situation. Since you didn't mention you had an EWG I'm assuming you dont and your IWG was unable to compensate for the amount of air the car was flowing. This caused the turbo to pressurize an excess amount of air. The MAP sensors saw you reached a certain defined limit and cut the fuel in order to stop the over boosting.
You learned a lesson; don't go WOT in high gears, always down shift. You can also inform eric of this happening and he can likely adjust the WGDC and TD tables to help prevent this (possibly even raise the limit since 21 psi isn't all that high). It's likely he wuill tell you to stay off WOT when in a high gear situation.