Practically all sailing vessels in use (some racing sailboats etc excepted) have auxiliary engines for moving in constricted areas like ports. Considering this accident happened with people up in the rigging, they were presumably hoisting or lowering the sails when the engine lost power and they drifted into the bridge.
I’ve heard (can’t tell for sure from the photos I’ve seen) that they were “dressing the yards” at the time - which is when the crew stands on top of the yards (the horizontal spars) side by side. It’s done for ceremonial or celebratory reasons, not for work.