I thought this was debunked, but the spirit of it is accurate. I'd guess the statistical swing wouldn't be from 85-113, but with such a large sample, be from 95-105 or even tighter.
Leaving aside the "south is stupid" arguments, notice that the "dumber" states there are poorer states with shittier educational systems. Both of those factors contribute to lower measured IQ scores.
Of course, having a local culture hostile to book-learnin' can't help.