If they tested the feed of course they would know the difference because the non-organic feed would be contaminated with pesticides/herbicides. And organic livestock is fed organic feed because of course the contaminants are reflected in the meat. This is easily verified as basic fact, though actually testing the feed or the meat is an expensive process hence the whole honor system.
This doesn't make organic a scam. Exactly the same reason you might not want an apple sprayed with a pesticide applies to eat a burger from a cow that was fed feed sprayed with the same. In many ways moreso given that these things are concentrated as you go up the food chain.
https://www.ecfr.gov/current/title-40/chapter-I/subchapter-E...
Conventional red meat can have 20X the amount of glyphosate than your apple can.
This was a failure of the certification and monitoring system. Often by design.
I don't buy organic. Too niche of a section and the risk profile seems low enough that it doesn't seem worth the attention to me. But I'm not threatened by it, as many seemingly are, and get why some people are focused on that. Years back I did subscribe to a CSA that followed organic principles not because of the organic element, but because their land use was sustainable and quite beautiful (most farms are dire factories, in essence, whereas this place was an eclectic wonderland).