I though he may have meant Portland, Maine,
I didn't think about Maine, though that wouldn't have been much closer than Oregon.
So, all this said, what did the OP hear?
This is one of the annoying things about MW these days. I'm fairly certain you could tune every channel on the dial and hear Coast-to-Coast AM on about two-thirds of them and ESPN radio on most of the rest. Makes it very difficult to ID a station. Virtually no one does local programming at night anymore.
As for KXEL in Waterloo, Iowa, they do get out. They can often be heard here in Washington state.
You must be in the eastern part of the state because it looks like KXPA has a lock on the western half. Even eastern Washington is outside the fringe nighttime pattern for KXEL, so that's a pretty good catch.
As for what constitutes DX, that depends on the DXer. They all have their own definition, really. It's a hobby, not a law practice.
True, and one's definition may well change over time. This is why I've always just logged what I heard and calculated a distance, letting the logging speak for itself as to how unusual it is.
I should point out that I'm really not trying to rain on anyone's parade. More trying to inject some experience and reality. I suppose I've seen far too many people bragging on how great their new radio is because it heard a 50kW flamethrower from 500 miles on a quiet winter night well after dark. They might have a great radio, but that reception by itself probably doesn't prove it. Not at all saying that's what happened here, just that it shows there's a need for a serious reality check for many in the hobby.
Just for grins I pulled out my old Sangean DT-200VX last night. It's got to be close to 20 years old, much of which was spent in my car in the heat and cold so I'd have a radio to listen to at lunch time. I couldn't say the last time I used it. I pulled in WBZ from Boston, 900 miles away, pretty much like a local. WWL from New Orleans, 800+ miles distant, clear as a bell. Admittedly, the DT-200VX is not a cheapy pocket radio, but it's still limited by the 2" antenna. I'm not trying to brag here, just illustrating the point that distance alone does not determine the noteworthiness of a reception or the outstanding quality of a radio.