"Mahara": odd "open source" project (GPL with paying code access)

I “randomly” landed on the web page of the “Mahara” web software, a sort of Moodle specialized in making students to collect and showcase their achivements and projects. The odd is that downloading/self-hosting the software and even browsing the git repository is restricted to subscription holders, as explained on this page.. Isn’t this in line with the GPL licence / open-source arrangement? I have seen in the past dual licences, but the core of the software was still available in source for...