Honestly, I'd not be surprised at all if people in an accident did not tell the investigator that they were not wearing their seat belt. If an anonymous poll were taken about whether or not you'd be honest about that fact if asked by LE after a traffic stop or after an accident, I would bet we'd see that the majority of the people would say they'd say they were wearing their seat belt. Two reasons: (1) avoid the citation for failure to wear seat belt and (2) avoid any possibility insurance may fine a clause to deny medical claims due to no seat belt.
In this instance, we know from the highway patrol testimony that he took the report from JY not MY. We know from his testimony that he did not separately question MY. Granted he said (IIRC) that she was nearby and could have disputed anything he said. Seriously, though, does anyone really believe she is going to dispute JY to the highway patrol right there in front of JY? Given they have just had an accident, she is pregnant and probably (naturally so) worried about the baby I'd expect her to just be ready for it to all be over with so she could calm down.
We also know from his testimony that he was not the first on the scene of the accident and that when he arrived both MY and JY had been taken to the hospital. There was already first responders that had been there for some time whom I suspect and IMO had taken their own perusal of the incident, formed opinions and IMO passed this on to the highway patrol when he arrived. We do know from testimony one of those already on the scene was the brother of a life long friend of JY. In a small rural community, this does go a long way in taking someone's word for an event or incident.
I truly believe the highway patrol report to be one of a formality rather than a full blown accident investigation. Since there didn't appear to be anything untoward on the surface, what was there to investigate. All accident reports are not a full investigation, IMO.
I'm not saying either the sheriff's deputy (brother of the JY's friend) or the highway patrol fabricated anything. I'm just saying I don't find it unlikely that they'd take JY's word for whatever he said happened and be done with it.
IMO