Logging in with Google after GitHub (and adding your email) results in 2 accounts
It's the ole oauth account linking/merging problem! I logged in via GitHub initially, added my email to my account. But then later, forgetting which thing I logged in with, logged in using Google and now I have two accounts. Though I used the same email address as my Google account.
No idea if the other direction does the same thing, but noting that GitHub login is the way for now.