This tweet doesn't tell us much without more context (I.E. what were Microsoft's expectations and what level of stock numbers have they made available to retailers) but it wouldn't surprise me if the pre-order numbers are good.
Ultimately, the Xbox One X is an enthusiast product, buyers of which will mostly likely be:
A) Devoted fans of the Xbox brand
and/or
B) People who want to consume every piece of new tech available
These two sets of buyers are also the most likely to want to put their names down to be first in line whenever a new Xbox comes out, no matter the cost.
The real surprise would come if it turns out that it has legs at that price tag after the initial hype dies down and most of the enthusiasts have already purchased their units.