Yes happened the same, i don't know if have nest in the area but now after some flight with attack to my phantom is surely that the reason.
Please tell me why i should lie? I'm 36 years old and in my city that is on the seaside seagulls are common. I'm not afraid of them but I've never had an experience like today where a lot of seagull follow me flying from the sky down really close to me. They know that in my hard case there is their enemy, my phantom. Because when i put back my phantom in it, they were still flying over me at a close height.
I'm not calling you a liar. Living by the sea myself, I've seen many things these Seagulls will do to obtain food both in nesting season and out of it.
Unless there was some food source, or you aren't realizing the length of distance you walked, I still find this hard to believe. Seagulls, especially during nesting, will NOT leave their clutch behind such a distance as 300m. They WILL protect it, all of the colony will defend even a single pair/clutch, but they will not leave it unless they ALL had a food source they were fighting over. Your drone was in the case and no longer a food source.
A few birds will often seem to be tens if not hundreds when a person is being warded off. The distance you had to traverse will also seem extreme in retrospect.
200-300 meters? Not likely. At ALL.