There’s a difference between summer and winter fuel for gasoline engines in some areas. It’s usually to do with smog restrictions.
The same octane can be reached with different blends of hydrocarbons. So instead of just ‘pure’ gasoline to hit a desired octane, refineries can mix together higher and lower octane fuels to reach the same overall octane rating. This increases the amount of refinery products that can be used to blend gasoline, so it can be made more cheaply. The trade off is that it’s less pure, and most importantly for this comment - that some components of of these cheaper blends may evaporate more readily, leading to smog.
In summer, when it’s warmer, some areas mandate gasoline must meet certain standards for evaporation. In winter, those standards are decreased, because it’s cooler.
Ethanol has a relatively low evaporation point. I don’t know the specifics of the commenter’s location, but I could see ‘summer gas’ having no ethanol to meet these standards.