It's misleading.
First, there are going to be plenty of people who played the original and are interested in the remake but do not follow enthusiast gaming sites and don't realize this remake doesn't leave Midgar. Hell, even on this forum, nearly every thread on the Remake includes a poster or two who hadn't caught the news about the episodic format yet. Second, there will be an even larger group of people who didn't play the original FF7 but know it by reputation, and some of them will be surprised to learn that this game titled FF7 Remake covers roughly 1/8 of the original (albeit in dramatically expanded form).
And you really think laying out the details for those people is going to change purchasing decisions?
If you think calling it a remake is disingenuous, then it's just as disingenuous to call it "just Midgar," since that makes anyone who played the original think they are getting a 3-hour game. So, basically, you would have to say "First part of an ambitious remake project to flesh out and expand on the story and world of Final Fantasy VII, beginning with a massively evolved Midgar chapter."
Saying "it ends at Midgar" almost certainly means something completely different in this game than it does in the original game. If it is a cheap 3 ~ 5-hour experience that doesn't turn Midgar into a whole game, then I'll be right there with you all calling bullshit, but I'm willing to give the vision they are selling a chance.