For being 15 year old, cool work!

But calling this de-anonymization is a stretch, if it can possibly pinpoint you within 250 miles (that's assuming geoip is correct too, which it rarely is).

In their GeoGuesser demonstration video, the higlighted area is densely populated and you still would need to match millions of people vs the online user.

It does provide some hints as to the location of the targeted user, and that is cool!