That's interesting. The Germans surrendered as well, but they may have done so with the intent of actually surrendering, and upon seeing the weakness of the people holding them realized they could probably break free, making it not perfidy on their part.
That being said, the Geneva Convention didn't exist when this happened.
To be fair, he was just responding in kind. Clearly the enemy soldiers had done the same thing while he was gone.
Overpowering your captors, even if you allowed yourself to be captured, is not the same thing as feigning surrender. Once you are taken into custody you are allowed to try to escape. There are no restrictions on taking your former captors prisoner in the process.
In a feigned surrender you never get taken into custody.
Perhaps he initially did genuinely surrender, only to launch an escape seconds later, but claimed otherwise after the fact because it made a better story. ;)