>A Vancouver man is trying to figure out how he managed to get into someone else’s Tesla recently and drive off

It's easy to figure out. The car was left in valet mode by the owner, a mode which is meant to only be used in lieu of handing a key to a valet. So it wasn't 'unlocked with their app', it already was unlocked and ready to drive. This is no different to someone leaving their keys in the ignition of a normal car.