One account seems to say this occurred in the channel between Salamis and the mainland.
The container ship was likely heading in to Elefsis to unload. Or there is a shipyard there. It was named Hellenic shipyard in the 1970s.
Possibly the minesweeper was going in, or out, for repair work.
Although this is where the famous galley battle was fought with hundreds of triremes, it is a very tight strait. One deep channel in a roadstead about as wide as the Thames in London.
It used to be that ships waiting for repair, or to be scrapped, were anchored haphazardly around the channel. Possibly o e of the two had to get around an anchored ship and this put it on a collision course in close quarters.
"These things must be done delicately-- or you hurt the spell." - The Wicked Witch of the West.
"We've got the torpedo damage temporarily shored up, the fires out and soon will have the ship back on an even keel. But I would suggest, sir, that if you have to take any more torpedoes, you take 'em on the starboard side." Pops Healy, DCA USS Lexington.