No, that's normal and just a characteristic of the nucleotide ref that NCBI BLASTn uses by default. There are lots of "uncultured" sequences in there, so it is almost inevitable (even with tutorial data, or even known reference sequences!) to blast to "uncultured".
There is an option of exclude "uncultured" when performing the BLAST search, but that's not important here. The important point here is that your sequences are matching 16S sequences (even if they are "uncultured"), so the query sequences that you are using are not the problem (and they should not be).
We're moving down the checklist:
QIIME2/dependencies are the correct versionsQuery sequences look goodPre-trained 515f/806r classifiers on QIIME2 website should work fine for the Atacama data
This all indicates that the data you are working with should work just fine. Please double-check that you are using the correct file paths for the correct classifier (download a new one just to be sure) and for the correct query sequences. You could try a different classification method (e.g., classify-consensus-blast) but this classifier really should work just fine with the Atacama data, so at this point I suspect the input files must have been mixed up at some point.
So please give it another try and:
Could you please share your taxonomy plots here?