OP was safe to grab some food quickly, what he wasn't safe to do was walk past the food outlets to go visit a lounge ...

Also, he already had his 20 mins before he started walking back to the gate according to his own post.

It is hard to imagine the flight being able to go from no boarding announcement to fully boarded, upgrade processed to fill his seat and door closed all within the time it took him to get far enough away from the gate to not hear the boarding announcement and return, if he indeed kept to the '20 mins'.

The restrooms and food are right there next the gate he would have been using and well within range to hear his name being called even if things had moved as quickly as claimed.

Hard to see the OP as a 'victim' really, had he asked, 'have I got time to go to a lounge' the GA would probably have said 'no'.

Also 'should be OK' is not a strong enough statement to rely on when you've already overslept, been woken by your boss and are depending on the next flight to make business critical meetings ...