It is a cliche but probably true: Second rewrite will be better by those sort of metrics even without a tech change. Lessons learned get applied. Domain is fully known. I definitely believe in fewer LOC with any not-react due to all the hooks, memo, etc. boilerplate though!
While I'm sure there were a few places where better decisions were made, I think it's reasonable to assume that the majority of the reduction in code is due to the different approach to front end development.