Part 91 doesn't really apply to model airplanes. It only apply's to airplanes with people on board, as mentioned in the recent NPRM. But that NPRM does not include model aircraft. However, I think it can be classified as endangerment to the NAS by impeding the FPV pilot's capability to see and avoid. Then again perhaps the model airplane can be considered a UAV under the proposed NPRM because it was operated in FPV mode violating the AMA's safety code.