This is—unfortunately—the expected behavior based on how the system is currently designed. The filters don’t distinguish between the Observation Taxon (what’s displayed at the top of the page) and the Community Taxon (on the right side of the page). Technically it is the species that is RG, not the variety.
But for all intents and purposes (filtering, exporting data, querying via API), it’s displayed as RG at variety because it is the Observation Taxon that appears in all those areas.
See existing report: https://forum.inaturalist.org/t/species-level-research-grade-attained-with-only-one-species-level-id/3270
and related feature request: https://forum.inaturalist.org/t/search-by-observation-taxon-or-community-taxon/3620