Looks like something that has been overlooked. We should improve the API to make this easier.
I am not 100% convinced that the resultID you're getting is from the STL export -- it looks like the result of running CompGeom or MassProp rather than just a simple STL export. Digging deeper, the only thing that creates a match to 'point' is write_degenGeomPointResultsManager() which makes me think that is a leftover from running DegenGeom before. Perhaps you did not do it intentionally, it may have been triggered by VSPAERO or ParasiteDrag...
If you run CompGeom first - then STL export will not create a new MeshGeom and will export the results of the CompGeom (whose GeomID should be reported in CompGeom).
However, if there is no MeshGeom in the model, STL export will generate an STL of the model (without intersecting components) and will export that. As you have noted, it does not delete the MeshGeom automatically.
I suspect that if you use a simple FindGeoms(), the new MeshGeom will be the last entry in the returned list. You could also FindGeomsWithName("MeshGeom") and if you don't have any other Geoms with that name in your model, it will be the one just created.
If for some reason those don't work and you need an immediate solution, you could run FindGeoms() before you call export - and again after the export -- and then figure out which entry was added.
Rob