Maybe some Belgian member can clarify, but I believe there are still some laws on the Belgian statute book from the time of the First World War that prohibits photography of all sorts on industrial and commercial facilities, including docks and shipping. Very rarely, if ever, used these days. I don't know if anyone other than law enforcement can enforce them, and it's unclear who this particular person was, but it's worth having this in the back of your mind. I was once stopped by port security in Zeebrugge in the 1980's from taking photographs while waiting for North Sea Ferries, and this came up in the discussion we had. Photographed in Belgium many times before and since with no problems.