I bought a 16/512 Space Grey 2018 MBA when it was released, then sent it back after taking it out of my bag several times and finding the battery completely drained. As you'll see if you search for a previous thread, there's no way to shut down the 2018 MBA, and mine rebooted as I carried it in my laptop bag.
I can find no evidence of this. With newer MacBook Pros and the Retina MacBook Air, the computer automatically turns on when the lid is opened or any key/trackpad is clicked, but turning it off and closing it will still turn it off until the lid is reopned.