I guess the mystery is solved. There's only one direct Thalys train a day from Brussels Airport to Paris Nord. 9:29-11:35. It IS on the www.bahn.de website.

Note that even this schedule takes 2:06, which is actually a few minutes longer than the 2:01 or 2:03 half-hourly service with a change at Brussels-Midi. In fact, if you miss the 9:29 departure by 2 minutes, you can still take a slow train at 9:32, and then catch up to the Thalys at Midi for Paris Nord.