You must be getting a false positive, because it is definitely not. The source for the website is on Github (and the website itself is hosted using github pages I believe), and it consists of one HTML file.
Hmm it is possible... I am getting the correct page now, where as before doing a curl was resulting in a 403 and invalid ssl cert warning on Firefox. User is also very new and has no other activity. When I tried it the first time it redirected me a number of different times. Something seems fishy.
The website is fronted by cloudflare to Github pages. The certificate comes from cloudflare so if there is an invalid certificate or an old cipher it is a misconfiguration on Cloudflare's end.