Lol! I don't agree that the euro would've been a better option given the current situation.
If they were to choose the euro or us dollar, then they would be at the whim of their respective central banks. The european central bank could print lots of euro and crash the euros price, in essence they would be under their control if they did that. The only way a nation like liberland could remain free would need to have its own currency or use one that isn't issued by a central authority.
Euro is complete shit and that has been proved on a national level. The US dollar is already controlled by a central authority and using centralized currency would get them to stay on a leash. Bitcoin as a national currency could be the best possible decision but Satoshi as prime minister is a rumor hahaha.