If you haven’t noticed by now Microsoft has started advertising directly in the Windows suite. In the Windows 10 app you might have seen a little “Get your Gmail on your phone”, which really is not all that annoying, but when you click the link it brings you to a landing page to download Outlook on your phone, not Gmail.
Yes, you can use Outlook on your mobile device and add in your Gmail account, but the way the ad is represented the user would think they would be downloading Gmail on their phone, not Outlook.
This is definitely questionable advertising by Microsoft, which is not all that surprising as they forced Internet Explorer on everyone and only after EU regulation and big fines that changed.
Currently this ad is visible for everyone in both Windows 10 mail as well as Calendar.