Android branding guidelines are very unlikely to matter at this point, given that it's descriptive use (not forbidden by trademark law in the first place) anyways...
> Descriptive Fair Use: Found at 15 U.S.C. § 1115(b)(4), the descriptive fair use defense protects your ability to use ordinary words to describe your own goods or services, even if those words happen to be part of someone's trademark.
https://www.dmlp.org/legal-guide/using-trademarks-others
Since the Windows Subsystem for Android actually runs Android, "Windows Subsystem for Android" is a product name and not just a description, and "Android" isn't a generic descriptive term in this context, it seems to me that Microsoft is using Google's Android trademark in a way that isn't protected as fair use.
Really I wasn't trying to name the exact defence but gesture at the principal that trade marks prevent competitors from using names that might confuse customers, but they don't prevent competitors (or anyone else) from talking about the product. It was just a coincidence that I used a word that happened to also be the name of a specific kind of fair use.