WvW Art of War Buffs
This player is close enough to the keep to receive the keep’s buff.
I think the buffs stay on your for a brief period after running from a tower or camp with them but I haven’t really paid attention or timed it.
Or putting it like this: For this very area I’ve been having the buffs from the keep until I was way off to the west of the keep. I assume it is normal, as I noticed it for months. I guess it’s “the bigger the keep the further the buff”. Or it is indeed timed as Durian said.
@Jenni, only the garrison had buffs on it, but wasn’t owned by the other server that the player I targeted was from. However, their server did have a stake on hills so their guild may have had a claim on that keep.
I noticed other players from the same server, same guild, without the Art of War buffs on them so it may likely be a timed delay. I searched for a similar occurrence of buffs remaining on players when they’re not close to a fortification, and found it might be related to the supply buff remaining on players when they leave a camp, for instance.