Thank you for sharing the link. Here's the relevant bit from the article:

Most gas stations don’t want to install new tanks just for E15. Instead, they’re installing blender pumps, which mix the ethanol and gasoline together in the right proportion depending on which one you want. But there’s a problem: if you pump E15 into your car, about a third of a gallon remains in the fueling hose when you’re done. If someone comes along, switches to E10, and buys a single gallon for their lawnmower, they’ll get a third of a gallon of E15 and two-thirds of a gallon of E10. That comes to about 11.7% ethanol, and that might be enough to set your lawnmower on fire.

So the EPA produced a new rule: if you sell E15, you have to require your customers to buy at least four gallons of gas regardless of what blend they’re buying. That’s a big enough purchase that the residual fuel in the hose is too small to matter