Somebody tell the Swedes they've successfully invaded Estonia

On January 12, the keepers of a medieval citadel in Rakvere, in northeastern Estonia, came under the national microscope after a rather embarrassing incident involving a successful Swedish conquest of the citadel. Unbeknownst to the Swedes, the citadel was observed flying the Swedish national flag by people in the region who quickly alerted the authorities of the apparent invasion. The citadel was to raise the Rakvere city flag in honour of its liberation during the 1918-1920 War of Independence, however the Swedish national flag was instead flown causing great alarm and subsequent embarrassment. Apparently the similar design of the two flags is to blame, though we'd like to think a Swedish prankster had a role to play in the easily avoidable mix-up. What's the Swedish flag doing laying around, anyway?