The site doesn't mention which meaning of "polyglot" the people behind it had in mind.

I assumed it was for people writing "polyglot" toy programs, because it'd be very useful resource.

I very rarely encounter uses of the term "polyglot" referring to people knowing large number of programming languages, so I didn't think of this use. Looking at it now, from this perspective, I have to say that I don't think it would be useful for these people, not enough depth.