Trickery?

[Nevadaref]

This happened in a tournament game for which I was an AR last weekend.
The ball is played through, but is clearly too far for an attacker to catch up to. B1 is following the ball as it rolls towards the penalty area. Just outside of the box the ball loses its momentum, and B1 realizes that it will not make it into the penalty area where his keeper could pick it up. Therefore, B1 drops down onto his stomach (prone) and heads the ball into the area.

I was the AR on the other end of the field. The keeper did not use his hands, but played the ball away with his foot. No action was taken by the Referee or the other AR during the game. My question to them afterwards was if they thought B1's actions constituted trickery to circumvent Law 12 per Decision 3 on page 27.