Hi @Enrico_Michelotti !
I'm very happy that you are enjoying HTM.Java and also welcome! More than it being any select group's or single individual's library, I'd like to mention that it is a community sourced and driven project for which we all can have a sense of ownership. In fact, you bringing up questions over some of the functionality is by all means a contribution in its own right, and we are all better off for it!
Now to your specific question.
maxValue is a "bound" marking the upper bound and by convention most often is not inclusive, and that is the case here. For example, a bound of 0-15 usually (by convention) means anything in the range of 0 (inclusive), and 14 (15 being the not-included [excluded] bound).
You are however correct that it is not very clear, and I think it should be documented that minVal and maxVal are inclusive, noninclusive (in that order).
That is both here in the Python version and here in the Java version.
If you'd like to open an issue to have that documentation improved, that would be great (also if you'd like to submit a PR to fix it - that would be great also... )