Is it unusual for an aircraft to flash its landing lights in sequence?
The flashing lights help to make the airplane more noticeable. They have also been suggested to reduce the risk of bird strikes. This is offered as an option or add-on for many types of aircraft.

In addition to helping the pilots to see ahead of them when on the ground in dark conditions, landing lights help to make planes more visible to others. The FAA requires landing lights to be on for commercial flights under 10,000 feet, and encourages pilots to turn them on at least when near an airport or in low visibility. Flashing the lights makes them less likely to be confused for something like a star at night.