What you saw were pulse lights. The alternating flashing pulse lights enhance situational awareness for other aircraft and make the aircraft more conspicuous.
You'd be surprised how many aircraft have these lights and use them. Some of the many pilots I know use them anytime they're in the air and some use them below 10,000 feet. Regardless, they make the aircraft more visible to other a/c.
Some can debate the effectiveness of these lights, but IMO they are very effective. Better situational awareness is an ever increasing challenge for pilots.
The more help we get for increased situational awareness, the better.