From quickly looking over the result I don’t see anything unexpected, the results all seem to have “pop” in one of their tags.
If you mean that you want to have only results where a tag is exactly “pop” (and not e.g. “pop rock”) I don’t think this is possible with Lucene queries. You probably could filter out unwanted tags with something like tag:pop AND NOT tag:rock AND country:us
The correct syntax is area:Italy AND tag:"progressive rock" (note the colon), and with that the result looks good to me.
The documentation says
(part of) the name of the artist’s main associated area
See Indexed Search Syntax - MusicBrainz . So ('d say that will find artist’s with the area set to Italy, but not those which have set the area to Rome. But I don’t know whether maybe hierarchical search is implemented here.
The folksonomy tags and genres, which you can see on the sidebar on the right of the artist’s page