The reorganize and rebuild are different things.
Reorganize: it’s a defrag for indexes. Takes the existing index(es) and defragments the existing pages. However if the pages are not in a contiguous manner, they stays like before. Only the content of the pages are changing.
Rebuild: actually it drops the index and rebuilds it from scratch. It means that you will get a completely new index, with defragmented and contiguous pages.
Moreover with rebuild you can change partitioning or file groups, but with reorganize you can defrag not only the whole index, but also only one partition of the index.
The update statistics is automatic on clustered indexes, but not on the non-clustered ones.