To add to that, I would say that simple forms of "porting" can be done without really understanding the overall architecture. You just need to understand each line (or a few lines around it) at a time. I understood the post to mean something like that, which sounds like a good plan here, to minimize the risk of adding bugs.

And in comparison, a "complete rewrite" would require a full understanding of the big picture design of the original code, come up with a perhaps different one in the rewrite, and keep the differences in your head as you go (or, forget about the original design entirely and solve it from scratch - and keep that in your head as you go). Far more work and risk, and it would have been a bad choice here.

If that's the case, it seems unlikely that they'll be able to get the hoped for performance improvements