The biggest question is why would someone carry 10+ BTC with them if they are also going to a country known for crime? Maybe this happened because one of them posted something on social networks, and maybe they really paid something with BTC in that country and thus drew attention to themselves.
However, there is another option that should not be ignored, and that is that one of the "friends" knew about all this money and decided to use this trip to rob a friend - and when it comes to so much money, nothing should be surprising.
The next time you want to tell someone that you own cryptocurrencies, remember what kind of risk you are putting yourself in, such things are not discussed with friends and acquaintances.