Oh these are easy ones.
He picks on Jackson and Reich’s manner(s) of speech. In effect, he’s imitating them. Yes, they’re really that annoying.
As for Rio Linda: Having lived in the Sacramento area for years (and remember that Rush first hit it big in Sacramento before he went national), I can best describe Rio Linda as a sort of poorer, trailer-park-ridden, cars-on-blocks community of what would be known as rednecks...if they were in the south. In other words....none too bright.
Also realize that Rush, back in those days, got more than his share of call-ins from idiots in Rio Linda....hence his denigrating reference to that joint to this day.
Hey! I resemble that remark. But actually we are hillbillies. The rest of the country has rednecks.