"during the first month of availability"
So capturing the period when all the fan-boys get their hands on them, along with those who want to try and buy a load to sell for a profit on eBay because Apple are forecasting the usual 'production issues, low supplies etc' to try and get people to place pre-orders..
What will be telling is sales AFTER the first month of availability. I think this will be a lot less encouraging as it's clearly a disappointing product by Apple standards, especially when compared to rapidly improving competition. I think for a lot of perspective buyers the X just doesn't meet exceptions so they're sticking with the 7, 8 or even checking out stuff like the Note 8.