That doesn't really jibe with the fact that it was based on Carbon (which of course didn't exist in NeXTSTEP) until Snow Leopard, so I don't think it's true.
It is true. The functionality of the macOS Finder is based on the NeXTSTEP file manager. You are talking about the API with which Finder was programmed for. Carbon was introduced for programmers to transition to Mac OS X.
It adopted features from the OPENSTEP file manager (column view, inspector vs Get Info) but I doubt shared much if any code with it. It was written in Carbon and IIRC built with CodeWarrior (at least at first)
