Judging from the content of the article, the problem is that Google's local subsidiary started on construction prematurely before the environmental assessment paperwork was complete (but after they already owned the site). Short of keeping a watch on the site 24/7, I don't see how the local authorities could have prevented that. It's possible that they may have been lazy and complacent, but absent actual evidence I doubt they were complicit.

Our society operates to a large extent on an underlying assumption that most people will not try to do anything blatantly illegal in plain view. Finland has just learned the hard way that this is not true of large American corporations.

No, it isn't an invasion. Google bought and owned this land, then started construction before getting the permits to do so.

This is like you buying a small vacation land by a lake in another country, then starting to build a cabin on it before getting permits to build. You aren't invading that country.