Passback or not?

I don't thing it fits the whole definition for backpass. It is "deliberately kicked" but not "deliberately kicked to the goalkeeper".
This. As I said before, the whole idea of this part of the law, is that when the player kicks the ball (which according to the Laws definition, means any time a player makes contact with the ball using the foot, including trapping it) it has to have been done with the deliberate intention that the ball should end up with the keeper. If the player does a slide tackle where the referee judges that the player's only motive was to clear the ball and the ball goes to the keeper accidentally, that is not a deliberate kick to the goalkeeper as envisioned by the law.

Similarly, if a player traps the ball but the referee's opinion is that the player was not aware the keeper was going to come up from behind him and grab it, that's not an offence either, which is why I would always err on the side of caution in such a scenario unless it's somehow overwhelmingly obvious.