Questioning a personality test skews you towards getting busted by the personality test police is what it does! I'm talking Meyers AND Briggs showing up at your house and kicking in your door. You gotta be careful!
For reals though, the matching dual-types that don't match the monotype is definitely interesting, especially for Grass - it doesn't vary as much as others between mono/primary/secondary typing, so that's a little unusual, but regardless, I have two standard possible solutions for this situation:
1) Go with whichever half of the dual-type is higher, and click the 2 or 3 at the top of the other one to get a different primary type.
2) Go with whatever description feels best to you, including under monotype. (I need to put a note about this in the next update, cuz I think this is actually the best practice in any situation)
Thank you genuinely for bringing this up and for sharing your results :)