Affiliate Marketing Secrets

I have an indoor antenna that sits on top of our television. The other day, I had it scan for channels (because I heard about a newer channel in our area, so I wanted to make sure the antenna / guide were up-to-date).
When it was done searching, one of the channels it found was 6-1 KOIN HD, which is the CBS affiliate for Portland, Oregon, but I live over 215 miles away in southeastern Washington state! How is it getting the signal? There are no translators for that station anywhere around, and there isn’t a need for one, because my area has its own CBS, NBC, etc. affiliates.