I'm thinking "covert op" for some reason.....
I say that something was put onboard the ship, probably in Kalinigrad. The 8 guys went out either from Öland or Gotland in an RIB, armed and took over the ship, pretended to look for something, but actually acted as escorts. They made sure the ship got to a specific place where another ship waited, they got out whatever they were smuggling, got it over to the other ship. Perhaps they had been promised they would be taken along, or they were simply offered enough money to take the roles as scapegoats/decoys and spend some time behind bars as a part of the deal. Whatever it was that they smuggled is now long gone and probably in the hands of someone who shouldn't be trusted to even use a squirtgun responsibly.