As far as I can tell all the articles refer back to Fair Trials, a real charity with a focus on access to fair trials around the world.
Their original article as far as I can tell is not on their website anymore but can be found at archive.org:
In the article they mention:
We even have reports of the imprisonment of a Swiss man for ‘possession’ of 3 poppy seeds on his clothing after he ate a bread roll at Heathrow.
So still not direct reporting of the actual incident. I have been unable to find anything with direct information about this incident.
That said, it is possible:
- Poppy seeds are banned from being imported into the UAE as narcotics
- There have been other cases of custodial sentences for small (albeit larger) amounts of poppy seeds (source is a newspaper in the UAE, presumably with direct knowledge of events)
- According to snopes, urine tests can return positive test for opiates up to 48 hours after eating them, so detection of small amounts is plausible
- The Australian government advises travelers to the UAE that positive urine tests can count as possession and the limits can be as low as 0.05g. I am unable to find these details on UAE sites, but I assume that the Australian government is reliable enough here.
Given that the person mentioned had presumably consumed the rest of poppy seeds on the bagel in the previous 48 hours it is possibly that detection of the small amount of poppy seeds and then a positive urine test could have lead to this scenario, however actual evidence of this happening appears to be limited to rumor.