Google puts random things in Spam, including ones marked 'not spam' or from otherwise reputable senders (like Github, despite receiving their emails for a decade). My monthly credit card bills occasionally are dumped in spam.
Its not really proof of much unless one is constantly getting junked
Back when I used GMail, Google would sometimes mark correspondence e-mails from Google staff as spam. Heck, I even had instances of responses to e-mails I had sent to Google staff marked as spam. Spam filtering is complex and clearly Google has (and continue) to tread a very fine line here.
Its not really proof of much unless one is constantly getting junked