My husband grew up in Detroit and said that isn't a thing there so he has no idea where Pizza Hut got the idea that it was a "Detroit style pizza".
My guess is that this isn't something that actually evolved in Detroit became a local favorite and adopted as a town staple, but something someone at Pizza Hut thought up, and the marketing team came up with the moniker "Detroit Style" to make it seem like an authentic thing, rather than something that a little executive **** dreamed up.
I further guess that when they came out with this, everyone in Detroit looked up, said "What's this sh
it, now?" And looked back down.
Still, it's not a bad pizza style. They cook up a deep dish rectangular pie with no sauce on it - just cheese and weird-shaped pepperonis with varying thicknesses - and after it's cooked they spoon marinara sauce on the top. I dump parmesan cheese on top of that, myself - but that's just me.