Title is inaccurate. It uses TeX algorithms, seems (LuaLa)TeX syntax too, and "modern standards". But those don't justify calling it a rewrite. "Modern TeX-inspired system" is a better fit.
Edit: I initially said none of the upstream maintainers call it a rewrite, but I was wrong because the original author did in fact use that turn of phrase on several occasions including in the manual and in a talk.
I agree though it's not an ideal way to describe it because it has some many differences too. It's not a port of TeX to a different language. As you suggest TeX-inspired is much nearer the mark. It's a from-scratch effort at addressing roughly the same problem space. It does re-implement some of the same algorithms. One of it's input syntaxs resembles TeX (although the resemblance is not even skin deep). But no it is not a rewrite, just a new take.