Man makes money buying his own pizza on DoorDash app (2020)

The original post that BBC links to has more interesting details. https://www.readmargins.com/p/doordash-and-pizza-arbitrage

Is this actually legal or is it a gray area that nobody has challenged at all? All I'm seeing is the restaurants themselves suffering the most, or left holding the bag - and it even seems Yelp is knowingly aiding the deceivers.