Catcher Interference on aborted bunt attempt?

[UmpJM]

Mike,

So, the question is, what do you call if the batter legitimately pulls his bat back after squaring to bunt - late enough that there is no way that he's going to try to swing and with no intent to contact the catcher - and the bat and the catcher's mitt come into contact?

Let's say a runner is attempting to advance on the play.

No intent by either player and the batter has had and unilaterally declined his opportunity to offer at the pitch.

What's the call and why?

JM