(unable to comment on the article directly for some reason)
Hi Brad,
I’m not sure this is (or was originally as its been going on for a few days across various services including Google, etc) Microsoft pushing these messages in error, it looks like it might be part of an exploit confirmed a few days ago by a researcher – https://abss.me/posts/fcm-takeover/
Many services are reporting the same thing and reddit is full of people expressing their happiness to receive such messages at all hours of the day/night across multiple services not specific to Microsoft.
Hope that helps. Cheers. J.