When your wrists are bent there's less room for internal movement.
The same site has some illustrations showing how the think keyboard trays should be oriented, and they have straight wrists: https://ergo.human.cornell.edu/AHTutorials/typingposture.htm.... (I don't like the page that much, since it doesn't show what I think is the best option: a flat keyboard with elbows at 90 and wrists straight, which you can achieve either with a sufficiently low desk, which I do, or a flat keyboard tray under a higher desk.)
I'm not Cornell of course, do don't take my word for it, but a tented keyboard feels 1000% more comfortable for me than this negative incline setup. Maybe I have to re-work my elbow angle.
Having your hands "tilting upwards" is very unnatural, and using your fingers a lot in that pose can/will quickly lead to wrist pain. Remember, most muscles controlling your fingers are in your lower arm, and the tendons that allow you to close your hand (or type) go straight through where your wrist and palm meet, which is exactly the part that is unusually flexed in that position.
Disclaimer: Not a doctor, just summarizing my experience and what I've read.
