See the info below that was received from the help at Edublogs to address the problem:

This student probably created their user account using your invite code and then created a blog.

If this happens the students can join a class by following the steps below:

1. Go to My Class > Join Class
2. Search for your class blog by entering just the first part of your class blog’s URL. For example, in this case, your URL is https://mrewert.edublogs.org/, you search for mrewert.
3. Click Send a request to join.

Once you approve the request to join the class in My Class > Student blog you will see their blog listed.