Silly of me to overlook that. But, they might also have a deadbolt for extra security when someone is trying go get in. I don't know--maybe someone else can chime in on that.
Also, I note the article says the plane was at 7000 feet, which means the call was probably made after the excursion to 43000 feet, which may have largely disabled anyone on the passenger side of the door.
Or not, cause I'm not a pilot and have never played one on TV. ;) Like I said, I'm just guessing.
It would seem that the excursion to 45,000ft would have killed him if he was in the passenger compartment.
Is it possible that he may made the call at 45,000ft out of range and that it didn’t connect until it was in range and then only briefly???
A little drop of Super Glue will defeat a key in a couple of seconds.