I loved Mythubsters but they were far from rigorous scientists (and Adam Savage says that every time he talks about Mythbusters to get Will Smith’s Tested some views).
Again, there are LOTS of variables involved including even whether the poppy seeds were washed or how sensitive the test is. My understanding is the disposable OTC-ish tests tend to be much higher sensitivity because they need to last a lot longer than chemicals in a lab.
Can it happen? Yes. Just like you CAN pop positive for THC from just walking too close to the stoners at a crag. But considering this was mass produced and processed salad dressing at a frigging costco? That is very much in the “oh god, I ate one poppy seed muffin!” territory. And considering that most of those arguments are geared toward people who will be unemployed if they piss hot, it is going to err on the side of caution.
Because there is a big gap between possible and probable. And you’ll note that almost all reputable sources say “it is possible and you should avoid this” in the same way that basically everything sold in California is potentially cancerous.
In fact, for Mythubsters in particular: I would need to rewatch that episode (… I need to rewatch most of their episodes, honestly) but they were always in downtown San Francisco, right? Could EASILY see a case where they got gourmet/organic poppy seed muffins rather than the insanely processed crap you find at a kroger (or a costco).
Going back to hemp oil and THC. From actual tests we totally didn’t misappropriate government lab resources to run, Bronners was incredibly processed and safe. But there was also enough variance bottle to bottle that I would never have (knowingly) risked it. We did basic statistics on the 4-ish bottles we tested but… money.
Whereas we also got a hold of some of the oil used at a local spa and that shit would have made Snoop Dogg dizzy.