I heard the sarcasm cristal clear when I read it the first time

This is not about about the naturalization process, or about naturalized Estonian citizens, but foreign residents. In the EU, if you’re not a national or EU citizen, you are not owed to vote in the local elections because you’re a legal resident. Previously Russian and Belarusian resident were graciously allowed to vote, and now this privilege will be rescinded. So I wouldn’t say it’s nationalist jingoism but common sense, Russia is actively engaged in hybrid warfare with the EU, and countries with a shared border are worried enough about illegal crossing from russian agent, so Estonia doesn’t need to grant special privilege to foreign citizens from a hostile country so they can mess with their local elections.