Each pixel represents quite a lot of area so aliasing probably isn't coming into it.
Bakersfield has a bunch of buildings (which lines up with the theory in my other post in this thread). It looks like imported land parcels make up a lot of the data in the Fresno blob:
You can also see the border of Massachusetts perfectly clearly, likely due to the import of MassGIS data. Surrounding states are all much lower density, until you hit Manhattan.
I wonder if it's because the streets are so gridded and therefore not as prone to aliasing.