Those comments were made in relation to remaking FFVII in the style of the PS3 tech demo and when it was presumed to be a single game. The first thing to note is that the game is now being done in PS4 quality graphics. Just re-creating every location, every PC, NPC, enemy model, VFX etc. from the original game in this level of detail & modern production values is a whole lot of work, much moreso than the original. Probably doable in one go, but that's not all this remake is.
The original game is a fairly linear journey across a whole planet. It's not particularly massive when it's done with relatively few pre-rendered rooms, corridors & spaces & a miniature world map with very little detail that are separated by loading screens that can move you forward as much as the developers need you to be moved forward at any given time with no reason to worry what is around or between those pre-rendered backgrounds, but if you make it with a more realistic scale & make it all more seamless, as more modern game design dictates, that expands the workload a whole lot. Now you not only have to model everything that was in the original game (which is a lot of work already), but you have to fill in a lot of the gaps. I'm sure the remake won't be entirely seamless with no loading screens or fades to black, but it will be a lot more seamless than the original. Now running through Midgar won't greet you with a loading screen every 10 meters.
And everything is in full 3d, not just from a single POV like the original. So where they could previously just model a single front of some building, now they might need to model it from all sides. And they need to model what is in the distance/horizon everywhere. Originally they didn't need to think about what is to the left or back of what you were looking at but now the player might explore his surroundings and turn his/her/their camera towards directions that were never shown in the original. What do you see when you look back towards the path you came from going to a certain playable character's home? This plus now all cutscenes need to be carefully choreographed, animated (both body movements & facial animation) etc. on a level far beyond the originals simplistic emoting.
Remaking FFVII also has a "problem" in that it has sooooo many unique locations with very unique characteristics. A lot of big games like Spider-Man nowadays rely on procedural crafting of the environments and a lot of recycling of assets throughout the world. It's the same trees, flowers, tables & other basic assets repeated a lot throughout the world. FFVII's remake can't do this. Even Midgar alone, the starting city, has you go from different levels of slums/poor residential areas to factories & high tech labs & brothels with lots of unique aspects that need to be hand-crafted from top to bottom without much they can reuse from anywhere else in the game. Imagine FFVII Remake being more like Uncharted where you push forward constantly and around every corner there is a new unique ancient temple, icy mountain, magical forest, asian city, chocobo ranch or such and they need to make a lot of realistic-ish scale connective tissue between those that makes them make some resemblance of a sense.
