It was this extended joke or perhaps real story, where a person as a child heard a two part saying like "Birds of a feather flock together" (not that one), but they misunderstood the second half as the name of the person who said the quote, like as if it was "Birds of a feather --Flocktuh Gether, 1857" (but much more natural and reasonable than this bad example)

Then they were confused constantly why everyone who every said "Birds of a feather" kept always attributing the author constantly, but nobody did that for any other proverb.

When they would say it themselves "Oh you know how it is. birds of a feather... ..." occasionally someone would be like "...[nods sagely] --Flocktuh Gether" and they'd be even more confused thinking the person was chiding them for not saying the author or something. And so on

The actual proverb was one where the first part made perfectly good sense on its own but distorted the meaning of the whole thing together, and the last part was a much more plausible name (like "April Showers bring May Flowers" <-- May Flowers is a pretty reasonable name, but the first part doesn't work on its own for this one). It's also a saying where sometimes people leave off the second half as implied and sometimes say it (like how you might often say "You can lead a horse to water..." but not finish it, sometimes you do though), which kept reinforcing that the person in the story wasn't crazy after all.