I'm not sure I would say that. I can see why they're not publicising it quite so heavily, but I can also see the point that people picking this up for the first time aren't necessarily going to be aware that it's not the full thing. That said, it's quite clearly a full game in its own right, so I'm not sure how much is actually owed to people in that regard.
I think I've flipped my thinking on this. Take something like Mass Effect for example - you go into that knowing or not knowing it's more than the first title, but it's just called "Mass Effect", even though the creators intention was always a larger story over a trilogy. Nobody really comes out of that experience feeling cheated even though the larger plot is definitely not resolved by the end of it.
I think we can apply the same logic to FFVII, if we get over the fact that the big difference here is that the media it's based on is one full title from a previous generation. But there are other pockets of media based on past stories that also don't indicate they're part of a larger story even though they clearly are - The Witcher is an example. Mass Effect isn't called "Mass Effect 1" or "Mass Effect Part One", and "The Witcher" isn't called "The Witcher 1", so I am starting to wonder why we all want to hold FFVII remake to a higher standard (myself included).
The more logical reason for them not making it "obvious" is that it's awkward branding (which they are no stranger to, hello duodecim 358/2 012 final remix prelude something) that would probably impact sales, even if only a little. But I think putting a small message on the back of the box is decent, and it's actually more than what I would expect them to have to do.
Also of interest is that I don't see it supporting a 4K resolution on there, but other boxes for games I have also say the same thing (HD 1080p, 1080i etc) even though they support 4K. So that doesn't really tell us much.