The Assimp binary in 3.3.3 was built from this commit
(2023-09-14). It includes all 5.3.1 features and bugfixes.
This fact is indeed not tracked in the LWJGL release notes. If a binding is updated to the latest version, but its version remains the same, there's no corresponding entry for that binding. However, if you check the commit log, the Assimp bindings were updated 4 times between LWJGL 3.3.2 and 3.3.3.
Assimp is one of the libraries that get very frequent updates and I try to keep up in LWJGL because I know how important it is for users, especially those working with newer file formats.