All source codes of games on puzzlescript.net
are hosted at https://gist.github.com/
Non-private publications on Github are public and you can always read and learn from the source. And I'm pretty sure you are always allowed, by Terms of Service, to "fork" these "gists".
The current culture is that puzzlescript.net encourages
you to learn from, edit and modify games hosted there using the "hack" button. If somebody doesn't want to distribute their source so freely, the practice is to "export" a game to a standalone webpage and host it somewhere not
(a common choice is itch.io
Lastly, it's best if the original creator replies but if your application is not proprietary and you're just creating something to play around or share back with the community, I'd say go ahead and use this game's source.