That ship most likely has a conventional right hand fixed pitch propeller. Most likely has a gear box for astern propulsion. At 8 knots it was probably at slow ahead. Ordering astern propulsion could take tens of seconds to change propeller direction. Now just because they lost power doesn't necessarily mean they lost propulsion. Dredging your anchors can stop you on a dime once you stop engine, depending on the bottom material. If they dredged both anchors for 3 minutes with no propulsion, I bet the ship would have stopped.