This wasn't just one single incident. I would actually claim that there's a significant amount of similar cases created by your team. So maybe you should look into this a bit further?

I created this overpass script to check these 15 municipalities that have Swedish as their major language to check if "name" isn't the same as "name:sv".
Some are of course just plain typos, but I would say that most are examples of Finnish behind the name tag, when it should indeed be Swedish.
https://overpass-turbo.eu/s/2dtP

A quick glimpse also suggest that a significant amount of these were originally created by your team. eg.

https://www.openstreetmap.org/way/1139157967/history
https://www.openstreetmap.org/way/640493457/history
https://www.openstreetmap.org/way/640388281/history
https://www.openstreetmap.org/way/1174678518/history
https://www.openstreetmap.org/way/165214296/history
https://www.openstreetmap.org/way/1139170291/history
https://www.openstreetmap.org/way/1174699122/history

These I found just by checking the 15 most northern issues of this Overpass Query of mine. So based on this I would estimate that about 50% of these errors could have been created by your team.