Questions you may ask

Why are there so few comments?

Because comments are often deodorant for smelly code: https://sourcemaking.com/refactoring/smells/comments

Why are there so few JavaDocs?

If you have an understanding of what the software is about and what patterns and frameworks are used, a class' responsibility very often becomes clear by its name alone - no JavaDoc needed. If you have an understanding of a class' responsibilities, the purpose of its methods often become very clear by their names alone - no JavaDoc needed either.

You should not have to read JavaDocs to gain understanding of a software - architecture overviews and an understanding of the domain (basically the game) are much more efficient.