But wouldn’t requireing two fluoridated carbon atoms instead of just one to qualify as PFAS, encompass less chemicals, thus narrowing the definition?

Allowing more things through, if I understand your analogy correctly in this case, is broadening the exceptions -- things not matched by the definition.

But, I'll bite, let's dive in. In a Venn diagram, substances with a minimum of 2 fully fluorinated carbon atoms is a subset of substances with a minimum of 1fully fluorinated carbon atoms, yes? Similarly, M&Ms with only red and green colors is a subset of M&Ms of any color, yes? If a person was to change their personal definition of acceptable M&Ms from any color to only red and/or green, would you call that broadening that definition?

The EPA definition would exclude chemicals like trifluoroethanol, so the EPA's definition is narrower, not broader.

From a strict organic chemistry perspective, trifluoroethanol contains a perfluorinated methyl group, and methyl is a type of alkyl, therefore it must be considered a PerFluoro Alkyl Substance.