Yes, the chair was in the conference/ signing room but it's likely an asset that was reused for other scenes. But those lights/ BG are definitely from the Versus trailers/ concept art.
Edit: It's likely that this could have been key art from 2014 before they overhauled the script and design.
Also about Verum Rex: It could very well be just an easter egg. Yet, why it sticks out is because it's an easter egg of something that didn't get to see the light of day. It's also labeled "True King", which is kind of a reading between the lines moment when a project that was just completed constantly used "Chosen King" as it's tag line. Finally, It's a full CG high quality scene that is thrown into KH that just gives a back story to an aspect of the "Toy Box" world. We haven't really ever seen this done in any of the KH worlds before.
That "leak" is really coincidental, if anything. The Nyx thing is kind of redundant, it would be expected if Versus was to happen Noct would be at the invasion like originally shown. If Nomura is planning on rereleasing FFXV as VersusXV, with his original vision, I'd be down to play it. It would be interesting to see how much the characters will differentiate (this is kind of the same realm as what Type series was going to do) and the combat will be likely be better, based on how it was supposed to be closer to KH battle system. That being said how funny would have been if this was Luminous 1st project they had to worked on and because Tabata had openly stated he didn't want to work on FFs (or atleast a main line) again this is the reason why he left.
