the instructions for using the page can be found on the page itself, if you don’t specify any parameters (https://jumear.github.io/stirfry/iNat_map). it should point you to the iNat API documentation, which will document most parameters accepted by the API itself. it also describes several special parameters that are used in the map page itself (not in the API).
this has to do with the way that particular map view is intended to be used. it’s really meant to compare a subset of observations with its parent set of observations, and although your case isn’t really that kind of use case, that view can accommodate your case as well, if you define the parent set as both A and B and the subset as either A or B.
since the primary set of observations in this view is, say, A only, the default interactive layer will work on A points only, not for B points. there is a second interactive layer that will allow you to interact with the combination of A and B, but you have to turn that on manually:
