It looks like he's comparing the quality and performance modes on the X1X. About the XSS performance mode he says:
"Series S' performance mode? Again, generally speaking, it's operating at a lower resolution than Xbox One X, even if its dynamic resolution lower bounds is higher and overall performance is more solid. The resolution window here varies from 1706x960 to the full 1920x1080. Variable rate shading is also used here - adjusting the resolution of points of the image, in theory helping to bolster performance. The pay-off is a mostly perfect 60fps."
If you care about 60fps the X1X does not offer the best experience. It was designed to offer games at higher resolutions and that remains true in this game. Not sure why there is an expectation for the XSS to deliver high resolution gaming when it was never sold on that promise.
It is also curious why there are so many XSS and X1X comparisons when those systems aren't direct upgrades. Still Tom says: "Settings-wise, near-to-far foliage draw is identical between One X and Series S, as is the quality of texture filtering, depth of field, and even shadows are comparable." That's impressive on the low resolution box. Coupling that with superior frame rates = a better experience at 60fps at least. X1X obviously takes the crown at 30.