here are some other stories that may have some photos for you to enjoy
https://www.cnn.com/videos/us/2019/06/09/seagull-maine-lobster-roll-photo-wxp-vpx.hln
https://949whom.com/a-maine-seagull-shows-a-tourist-whos-the-boss/
https://fox23maine.com/news/local/seagull-swoops-in-to-take-tourists-lobster-roll
Looks like intentional feeding. The ones here on the beach do the same thing if you hold food out that way. Locals have trained them all with French fries. Once the oldest gull swoops in to show the young ones that its safe they all fly past and grab fries as fast as you can lift them in the air.