What did I do? Am I being raided?

I just had immigration officers at my door. At least, I believe, they were from immigration. They showed me their ID and there was a bunch of them with my apartment number and the numbers of the other teachers in the block, written down, BUT, you don't actually know, do you? I mean, I don't know what immigration ID should look like.

So, naturally, I was worried. Well, a little bit, I was mainly annoyed because they were stopping me from showering and drinking tea before rushing off to work. The tea before work is VERY important.

Anyway, they checked my gaijin card and passport, made a phone call, jotted down my gaijin card number and, luckily, one of them spoke a bit of English which was used alongside the Japanese they used to explain to me!

My understanding was that Koreans are committing a lot of crimes around stations so door to door checks are now being made. Or something like that... Odd start to the day anyway, seeing a bunch of immigration officers outside your door.