Most of us rarely write such formal letters. I don't remember when is the last time I've written something as formal for a Finnish recipient.

At school I was taught to use "Dear Sir or Madam" or "To whom it may concern" but neither of those sound natural, they're just learned. If writing for a Finn, I just start with "Hei" ("Hey") (in fact that has lead me to start emails in English with just "Hey" as well). I may have used some other formality once or twice in my life when it was required for school or such matters but not as an adult.

So it may be that they were out of their element when writing that email and just put the first thing that came to their mind.