You may not know but your github email is publicly available. This extension makes easy to view anyone's email on their profile page. The idea is taken from a 2014 post that describes the method to see the email.
This extension simply fetch the public data from the user, parse and extract the emails and display them under the user information. You will find other emails than the user, it's because the script does not make a difference between the current user and another contributor.
How to prevent this ?
You may want to remove your email from your activity, github's solution can help you switch for a github email instead of your own.
MIT