Auto theft is not defined by the manner in which the vehicle is stolen you are correct.
What I beleive is being suggested here is insurance coverage limitations based on percieved owner negligence.
If you drive up to 7-11 on a cold morning to grab a coffee and you leave your vehicle running with the keys in it and its stolen you are liable because that is an offence in many States and Provinces.
If your residence is broken into and they take your keys from the inside the residence and steal your car your not liable.
There was an issue with some of the higher end vehicles having a plastic Valet key built into the owners manual sitting in the glove box. Kind of like a credit card with a key cutout that could be used for Valet so they didnt get your whole key ring with house keys. In this case owners were not liable because most didnt even know the key was locked in the glove box.
But some insurance companies made it tough to make claims.
Bottom line, check your insurance.