Hmm, where is that change log? On the NCH website? I think that may be automatically generated based off our commit comments or something, meaning it's not particularly readable for non-NCH developers. Probably wait for us to write a proper release note on this forum (I can do that today).
To answer your question to the best of my ability though, "VPClip architecture" changes means we have been doing a lot of non-user-visible work on the underlying architecture of our clip class. The old design was very prone to speed-change related bugs, and we've been fixing those kinds of bugs over and over again. Hopefully these changes make things less bug-prone for the future.
New level caching I believe is just an improvement to the way effects are cached. Without going into implementation details, it should be faster.