Finale doesn’t really support tremolo notation, as I understand it, and so multi-note tremolos are indeed notated in Finale using tuplets. As such, the MusicXML file exported from Finale also uses tuplets to notate those tremolos. It’s not impossible for us to add special heuristics to try to detect these kinds of workarounds resulting from Finale’s comparatively less semantic data model, but it’s not something we’re in a hurry to do.