The author just commented [0] to mention everything is CC-BY-3.0.

[0] https://news.ycombinator.com/item?id=41515968

I think this website has been around long enough it probably comes from the ‘everything on the internet is free’ era.

Sadly, today that often interprets to: someone bought (or just claims to have) the rights and now makes a living suing people for using it. If you plan to use it for anything serious, it's worth the effort to find something with an actual license.