maybe it was a cargo plane burning diesel
Aircraft don’t burn diesel. Small airplanes use gasoline, similar enough to auto gas that some planes use auto gas - with some limitations. Larger aircraft are turboprops, basically a propeller on a jet engine.
Also, minimum legal altitude is 500 feet in rural areas and 1,000 feet in congested areas except near airports. Looks like they were low. I have a problem with that around here, too.
nacl