Sounds like a random anomaly, unless you can reproduce it. One of the computers got confused.
I will agree that the triple honk when powering down is an error that should not happen (mine has never done this). But your second example is working perfectly. It is detecting that you left the car without your key (door opened and closed with your bag in the back seat). The triple honk is trying to say "Hey, your forgot your key, anybody could come along and drive me away".Another example of the keyfob sensor not working well is when my keys are in my bag, which I normally put on the front seat. When a passenger gets in the front seat, the bag goes in the back seat. If I open and close my door, a triple honk occurs. This shouldn't occur because the keyfob is still in the car.