Pretty sure that's just their way of saying "hey, if you want the Pixel, it'll work just fine on T-Mobile!" in counter to Verizon's advertising building the impression that it is only available on Verizon's network.
Verizon will have at a minimum secured 90 days of exclusivity to make it through the holiday season. Possible Blue, Magenta, and Yellow will get it? Sure - but it'll be a bit if you want to be able to use their upgrade programs.
Then again, T-Mo has been pretty creative... maybe they'll find a way to have you buy it from Play, then they purchase it from you and resell it to you over time lol...