That's very interesting, and it certainly bears further investigation. I suspect the affair is probably linked to the political goings on at the time in the region, the Allies having started off by backing the Chetniks, before deciding to throw their weight behind Tito's Partisans instead. I also suspect the equipment, which was presumably visible and could be photographed, would be the radar fitted to Dog boats, which would have been top secret at the time, and something they would not have wanted to fall into the hands of the Germans.
Just to add: there are lots of books available on the subject of Special Operations Executive (SOE) that would likely cover the campaign in Yugoslavia amongst the Partisans, so I'm sure it would be possible to determine which special missions likely involved the Coastal Forces boats.
This primer from the BBC web site: Partisans: War in the Balkans 1941 - 1945
provides a useful introduction to this complex subject.