Correct me if I am wrong, but I witnessed this incident at Beauvais two years ago.
A Ryanair was on the ramp preparing for departure, the steps were still down and baggage was still being loaded. The red anti-collision lights came on and the ground crew chief evacuated all his staff away from the aircraft. A lot of verbal was exchanged between the cockpit window and the ground with the crew chief refusing to allow his guys near the aircraft until the lights were turned off. The captain even got out and came down the steps to continue their “discussion”. I took it that switching on the lights was a signal that the engines were about to be started and the crew chief was simply protecting his staff. The lights were eventually turned off, and normal service resumed.