If you download those files, you can look at the provenance information by dragging and dropping them onto QIIME 2 View.
You will see that these files have had some basic filtering performed:
- cull-seqs on the full length data
- filter-seqs-length-by-taxon
- dereplication
I will say, that if you are interested in making an amplicon-region specific classifier You probably do not need to run filter-seqs-length-by-taxon. Just dereplicate, extract the region, then cull / dereplicate those sequences. See this example post.