Drug sniffing dogs can tell the difference. While drug dogs may not be able to smell it in edibles, they can definitely smell the oil. I doubt JA wants people bringing their own, and again this is really bad advice. How real will it be if/when someone gets caught? What if it's found in their possession in their home country and it's not legal?
For example in Amsterdam your are allowed 5 grams of cannabis on your person for personal use. However, oils made by chemical extraction are banned. There is a big difference in potency between traditionally made hash and the oils people put in those pens.