50 or 100 years ago, gas was distilled from native oil, and consisted of a mixture mostly of Octane and Pentane.
The invention of Cracking, and TEL, allowed “refineries” to create gas out of a mixture of different hydrocarbons. It is given an equivilant Octane rating, but it’s just a mixture of stuff, adjusted to run right. You can say that if it isn’t adjusted right, it doesn’t run right (and can destroy your car), but you can’t really say it can be “contaminated” with ethanol, because it is never “pure” of ethanol to start with.