Under Dell's support page in Drivers and Downloads the words "Apple Mac OS" appeared. If you go under product model and pick something out and then hit go you should see the same screen like shown above. Then just select the drop-down menu 'Select an Operating System' and what do you see? Well, for me, I don't see 'Apple Mac OS' anywhere in sight so maybe it is just hiding. It looks like Dell must have taken it down or Engadget is playing some stupid joke.
Most likely, this was some type of prank or an error (doubt it) on Dell's part.
*Update: For product choose the Latitude and for type choose the X1 and it the next arrow. Then look at the OS drop-down menu and you should see Apple Mac OS.