The world of VII shares very little with the world of X, even if the planets are completely different the physics of the universes simply do not match up.
- In VII there isn't a single pyrefly in sight, Summons behave differently with no equivalent of fayth, nor is there an equivalent for the farplane, and people don't require sendings on Gaia to avoid becoming fiends. You can literally walk into the farplane in FFX, again, something with no equivalent in VII, else the whole "very important person being dead" thing may have played out much differently.
- In FFX, there's no such thing as Materia or Mako despite there being tons of dead people floating around everywhere, which would be a disaster case in FFVII. Were it the same universe, anyone who walked into Zanarkand (or the farplane) would have likely died from mako poisoning.
If this is a real connection stated by SE, then it was very clearly made up after the fact likely on a whim, with no intention of it happening during either FFVII's initial writing or FFX's.
I put nothing past them for FFX-2 though, it was on a completely different level story wise, just like that terrible novel they wrote and called canon. And if these are the same people who butchered VII's lore to make Advent Children / Crisis Core / DoC happen (and later FFXIII lol) then i'm not at all surprised.