Stoichiometric is a fixed number. It is what it is. NO performance engine will run under power at stoichiometric ratio. Cruise maybe, under power no. It is too lean to make power.

Nitrous motors make best power at the same A/F the motor makes best power. So if your engine performs best at say 12:8.1 and you decide you want to spray, THAT is the A/F number you tune to.

As for the video, it is easy to see the sequence of events if you watch and listen. When the nitrous first hit, the ECU compensated and it went dead rich. It cleaned up a little, the rpm jumped, it made power, hit the limiter and then pushed a head gasket.

Doubt the motor was even hurt other than the head gasket.

Monte