Sure. And I think you can host your own HTML/CSS/JS on Wix too.
It's reasonable to blacklist a whole range of solutions that contain the ability to be used as template engines and then insist the students use something else.
I don't think it's reasonable to blacklist the most popular VCS website used among developers. It's a competition for devs, they _should_ be using version control.
All it would take is a cursory glance by another dev to know if they used templating or not, which I would consider baseline for a developer contest.
The article says their teacher just seen it was on GitHub and disqualified them off the bat. Unreasonable imo
They hosted it on GitHub. Not stored the source there. Hosted it.
Besides, I would say that teaching people how to use version control is good. But there are lots of non-GitHub solutions. Prefer those for students! Teach them the fundamentals.
It's reasonable to blacklist a whole range of solutions that contain the ability to be used as template engines and then insist the students use something else.