Also, just because they fool the particular testing tools that labs use doesn't mean you as a consumer won't have an adverse reaction to whatever it was they put in to the honey.
The problem with adulteration isn't exclusively limited to harmful health effects either. Even if your health would not be adversely affected by the adulterants, you might still want to be certain you're getting is genuine.
Let's say you bought corn syrup while under the impression that it was honey. It might not harm your health any more than any other corn syrup would, but you've still been defrauded, and what you got might not have the same health benefits that honey has (assuming honey has such benefits).
Your purchasing decisions could have an ecological impact too. Effectively subsidizing the growing of corn by mistakenly buying corn syrup will have different ecological consequences than subsidizing the establishment of more bee colonies by buying genuine honey.
That's not to mention the ethical issues of being conned in to giving money to fraudsters versus giving it to honest business people.
One of the interesting things I learned from the honey article was that fraudsters have figured out how to work their way around tests, at least for honey. I wouldn't be surprised if they could do the same for olive oil and other food products. It seems like a cat and mouse game.
Something not mentioned in the article is that testing labs themselves need to be tested, certified, and audited. There have been some scandals in forensic labs where techs have repeatedly falsified test results for decades. This is probably especially a problem when organized crime is involved.
If you are at all interested in food safety, I highly recommend "The Poison Squad", about the foundation of the FDA.[1][2]
[1] - https://www.youtube.com/watch?v=euBoKIm1v6Q
[2] - https://www.youtube.com/watch?v=s0rKnxm3X7M