I dont get it. If there are still players left then he's not the only high human?

They may not be "humans". Those other players, who've already died and reincarnated in the new world, may be of other races. And if they are saying he's the only remaining high human left, the other reincarnated high humans may have already lived out their lives. Or have gone MIA. ╮(￣▽￣)╭

Oh yeah. That totally makes sense. Player who died in the game permanently, but got reincarnated in the game will not be considered as high human as they are now part of that world. That makes sense. Thanks

I think there was no high human remaining after him, no one lived out their life. They were gone the moment the game ended. Thats why they just disappeared. But NPCs remember them.

No, there were only the 6 high humans (devas) to start with, and only a small percentage of all players were put into the new world. I'm pretty sure none of the 6 devas died in the game (to potentially be reincarnated) so it's likely they got to escape the game after Shin solo'd the final boss, Origin. Shin is still a high human, and the other players he met are still high elves, high lords, et cetera.