Says who? The fact of the matter is that the original Xbox One is so underpowered that the more powerful graphics processor can run what the original could at 4k. It will still be vastly inferior to the PC, ultra turned down settings. Also you notice all the stylised games that they showed? There is a reason for that, all the Xbox One X is rubbish graphics at a higher resolution.
one thing total biscuit pointed out, only one game was mentioned to have 4l60fps and that was forza. everything else is probably 30.