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What you're seeing on the airfilter is pretty normal.
The air supply into the airbox only focuses on a small area. If you don't have a new air filter handy you can rotate it 90-180 degrees so the fresh air blows against a "cleaner" spot.
I was told the opposite and not rotate the filter, as I used to as well.
The air comes in on that spot but then goes around the chamber through the filter then into intake, so more clean surface area on the filter the better.