You obviously didn't bother to read the case you're talking about. The crop in question was 95-98% Monsanto product, from hundreds of acres of land. The initial seeds may have fallen off a truck somewhere on the farmer's land, but to obtain that level of genetic purity, the farmer must have acted intentionally. That's what every Canadian court that heard the case concluded. He realized there was Monsanto product growing on his land and he harvested and replanted the seeds, knowing exactly what it was.
If the farmer had merely harvested the crop growing on his land there would be no issue.