Probably thought you were there still. The powered tailgate will be an adjunct to walk away locking. That can be a little temperamental least in the
Ateca. May be dropping the tailgate then does a handover to check whether the keys are still present and that can get lost. It would not want to put a lock instruction in to all doors if the trunk was moving say. Might be deemed you haven't left yet. Might be some algorithm of how it passes control between systems and that one has a hole in it. Needs some budding youngster to do a flow diagram

. Keep the kids busy. Scientific experiment.