When you're not a Hebrew speaker and you don't interact with Hebrew script, and you're developing a PDF library by yourself, it's easy to not even realize that there is something about it that you've overlooked.
In any case, Hebrew is handled differently from other RTL languages, hence this bug report in PDF.js: https://github.com/mozilla/pdf.js/issues/20097
Almost certainly something a smaller team would have never caught, given that a team with a massive name behind them didn't.
I don’t see dotancohene say anything about how surprising it is that that bug exists. They only say something about the judgment of it being an edge case.