So, it turns out if you're travelling via Dubai and you have a tiny speck of cannabis on the bottom of your shoe – we're talking 0.003g here, such as you might get walking any random place – you can not only be arrested, you've got a great chance of getting put in jail for four years. Oh, and poppy seeds from a bread roll? That's a jailing too. Melatonin, you too. Now, watch and be amazed as I never, ever, EVER, fly Emirates through their hub.
(And remember, this whole travelling-on-Emirates-through-Dubai thing is a core part of the country's economic strategy – Emirates is not just a random company that happens to be based there.)
This all goes to show that “zero tolerance” makes for great political campaigning, but is really quite stupid in literal meaning – you can and will be contaminated with drugs from your normal public interactions, even if you never even meet a user themselves.
A cute-but-pointless test-out of a drug detection machine over here showed even the doorknobs at Parliament had detectable traces of class A drugs.
Without applying a reasonable minimum amount, it is simply not accurate to assume that the subject had anything at all to do with the consumption or trafficking of drugs anywhere, let alone that there is any way they could have done that in or through your country.