Very strange behaviour of SKPhysics

Question

I have this code

SKPhysicsBody *firstBody, *secondBody;
if (contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask) {
    firstBody = contact.bodyA;
    secondBody = contact.bodyB;
} else {
    firstBody = contact.bodyB;
    secondBody = contact.bodyA;
}

I've captured this screenshot from my -(void)didBeginContact:(nonnull SKPhysicsContact *)contact method. I find it very confusing, because 2 & 3 == 2, but 4 & 3 == 0. As mentioned in docs,

If either comparison results in a nonzero value, an SKPhysicsContact object is created and passed to the physics world’s delegate.

I wonder how it is possible? Since second expression returns 0, why the delegate method is called?