It was legal. Do we now convict people because they were simply close? If someone say ate some hemp that had say a 0.01% THC content show up in their blood analysis, then we should prosecute them under schedule 1 drug federal protection laws then, right?
We currently do prosecute and convict people who are below the legal limit. O.08 is more of a guideline then an absolute, as everyone has different physiology and thus are impacted by inebriation in different ways.
This, combined with the failed field test is pretty damming evidence.
Ignoring the fact that you would have to heat pounds upon pounds of hemp to achieve a detectable amount of THC. We always have and still do convict people over incredibly nominal amounts. For most of history it's been a pass/fail test with no discrimination over actual amounts.
People very often are not charged when double the legal limit. People very often get charged when below because the field sobriety tests are designed to be both confusing and difficult to do for even the most sober person. I have zero faith in the field test in general from fallacies like I pointed out before. Also include that with the incentive that police have to have arrest and conviction records to proceed in their careers.
It is really easy to defend these collection methods until you have to fight them on wrongful convictions.
His BAC was 0.076 and 0.079. Being 0.001 below the legal limit doesn't seem like a great defense.