[Tobs40]

Author here.

The position is White to move, so even if the b2 pawn was not pinned by a white queen to the black king, it could not move. The b2 pawn is necessary to shield the black king from checks as this position is White to move - otherwise it would be illegal.

Also, rest assured, I checked everything thoroughly. There is indeed no way to squeeze out more than 218 legal moves for White here, but it's fun to try and I'm glad that people actually care about my article, didn't expect that, haha ^^