I believe you are stating that Score0to2 one-sided strategy should measure worse than plurality one-sided strategy. I don't think this is an obvious claim. It seems to depend on the underlying distribution of candidate quality (especially correlations of preferences).
I don't know what is up with 1-sided score vs 1-sided approval. That is an interesting observation you made and does look suspicious; we should expect the distortion of power to be greater than the loss of honest expressiveness.
When I looked at this project a year ago, I found other strange behaviors that led me to ignore its results, similar to how you are comparing its graphs to your intuition. There is no "correct" model in voting theory. Models are neither good or bad, only to the author's taste or not. For example, with voters on a single dimension, should utility of a candidate be the squared distance, or the absolute distance? How should a candidate's positions be distributed, is n-dimensional Euclidean space good? Should some candidates be straight-up better than others, and what should the distribution be? How should voters be clustered, if at all? What does "strategic" voting mean in each context? What does "honest" voting mean in cardinal contexts?
The author's discussion of methodology was lacking, and the missing priors make its results partially meaningless. I also had no success looking through the code for even basic behavior, because it was too hard to navigate. However, this is only a graduate project, and most graduate projects (including mine) are of lower quality than this one, so I wasn't upset.
In score systems, voters can sometimes be made honest to an extent. For example, on a book rating site, you probably don't rate all books 0 or 5; you use the full scale. Your ratings have greater self-value than your desire to tip the global score. While your assertion is reasonable that it is not the expected "honest" voting behavior, it is also a behavior worth looking at. This goes back to discussion of methodology; all these assumptions need to be documented, rather than buried in hard-to-read code.