How is Master Xehanort a portal?

[Veevee]

Hey guys,
seriously, I don't get this. They talk about Xehanort being able to time-travel which makes him, according to the game's logic, to a portal itself. Then Sora takes that information to leap ... into? Master Xehanort where he finds the latter's origin world and battles him. Maybe I got this totally wrong, but this doesn't make any sense to me. Xehanort being able to time-travel is far from being the same as him being a time-travel portal HIMSELF, so how does this work?

 

[Recon]

Nomura: “You should be able to understand”

To be frank, I really don’t know. Something something time travel.

 

[Zul]

I think they were able to basically force him to use his own time-travel ability and joined him in the transition. I do think it's a little messy in its implementation though.