That's only 1 of 3 pieces of data. If they only used the one you mention, then you wouldn't get the red/blue divide, you'd instead get a small/large state divide.
What this study does to get the red/blue divide dividing federal revenues by state revenues. So low tax, low spending states look bad because the Federal inflow is a bigger percentage of total spending.
What this study does to get the red/blue divide dividing federal revenues by state revenues. So low tax, low spending states look bad because the Federal inflow is a bigger percentage of total spending.