Arcade physics collide separates even if processCallback returns false.

[aivins]

If you do this:

collide(
    someSprite,
    someTilemapLayer,
    function() {console.log("Collided!")},
    function() {return false}
);

Parameter 3, the custom collision handler, will not fire because parameter 4 always returns false. As documented. However the separation happens and someSprite does get blocked.