It wasn't plug that I can see, the foam bottom looks like it is a lot more restrictive to the air flow than the standard paper type Wix full size element is
I looked back on my fuel receipts from before the engine service in January 2018 and the last two fill ups since I changed that element, it definitely got better fuel mileage with that element from installation until I changed it
I live in central Oregon, Bend, where the highway departments put cinders and gravel on the roads in winter for traction on the ice which turns into smaller dustier particles after driving on them all winter long
My truck is stock, no mods at all, it is my daily driver and stays on the pavement 99% of the time, I live on a dirt road so I have to drive about 200 Ft on dirt to get to my rear driveway where I park it. I use the same source for fuel year round but we do have winter mix on diesel fuel here due to the freezing temps in winter, I use a fuel additive to stop the fuel from gelling in the winter but that doesn't always work when it gets really cold (-25F) here