I would check this link out and see if it covers the difference:
https://www.inaturalist.org/pages/how_inaturalist_counts_taxa
There are some previous threads about this like:
https://forum.inaturalist.org/t/my-observation-and-species-counts-dont-match-in-all-observers-view-vs-my-observations-only-for-the-same-location/27264