Here’s his justification, so he doesn’t have to make one up out of thin air:
On 22 April 1808, during the Finnish War between Sweden and Russia, a Russian army landed on the southeastern shores of Gotland near Grötlingbo. Under command of Nikolai Andreevich Bodisko 1,800 Russians took the city of Visby without any combat or engagement, and occupied the island. A Swedish naval force rescue expedition was sent from Karlskrona under the command of admiral Rudolf Cederström with 2,000 men; the island was liberated and the Russians capitulated. Russian forces left the island on 18 May 1808.
So, you see, it was Russian territory for almost a month.
Its position in the middle of the Baltic Sea and more or less off the coast of Kaliningrad would make it an excellent military outpost from which to control shipping and spy on their neighbors.