[AZ] McDonald's parking lot: I was backing into a spot when the other pickup truck driver pulled into the spot as I was reversing in and I hit his tire. Who is at fault?

Little more detail: Him and I sent each other pics of the damage/drivers' licenses/insurance and both sent each other a text saying that we agreed on what happened. Neither one of us admitted fault because we both agreed that we weren't sure who fault it was, we just agreed on the events prior to the accident.

I know this has nothing to do with liability, but in case you're wondering: No damage to his truck/tire, but my bumper is cracked and will need replacing. I don't believe there will be any hidden damage due to the speed of the collision, but you never know