Some Polish journalists obtained documents relating to recent joint military maneuvers between Russian and Belorussian troops. The documents showed that these exercises included simulated use of nuclear weapons against Polish targets, and an amphibious landing by Russian troops on the Polish coast.
This all makes sense to Russians, because Poland is now a member of NATO, an organization that was long considered an archenemy of Russia. To most Europeans, that ended with the dissolution of the Soviet Union in 1991, and the end of the Cold War. But for most Russians, 1991 was a defeat, and not an end of the struggle against "the West." East Europeans are keenly aware of this, which was why they all wanted to join NATO. That gave them the protection of "Article 5" (in the NATO charter, which stipulates that an attack on one member is considered an attack on all.) But Russians see NATO as an aggressor, not, as the NATO charter proclaims, as a mutual security arrangement.
Poles see the revelation of the simulated use of nukes against Poland, and the amphibious attack on them, as a Russian warning to not cooperate too closely with NATO. To the Russians, NATO is a conspiracy to surround, and eventually invade, Russia. While this is seen as paranoia in the West, it is taken as an article of faith in Russia. And there's no arguing on matters of faith.