As the help text below it says, that's specifically for EA Profiles (which are the profiles at that link). It'll only accept a link to one of those; if you don't already have one, you should create one!
To explain why I downvoted, I don't like this general kind of response (i.e. "shouldn't this be part of large organisation X?"):
More precisely, it was started by a student who came to volunteer in Oxford one summer, had the idea and then created it over that summer and afterwards as his brainchild, fundraising to start it as a staffed-up charity, etc. CEA hosted a number of students who came to do volunteer work over summers and other free periods. So while it was labelled an 80,000 Hours project, it's appropriate to use it as an example of someone with little relevant experience starting a charity.