The bird cardinal derives its name from its red plumage, which reminded some folks of the red vestments worn by certain Catholic clergy.
Title should have specified: “not the sports or feathered ones”.
Seriously, though, I think a lot of people simply don’t know what role Cardinals play in the Church. Even many Catholics try to fit them into the hierarchy of Sacred Orders (”deacon, priest, bishop...cardinal?”).
As the article points out, their role is really more bureaucratic and advisory than anything else. It’s a shame that they aren’t given their symbolic “galleros” any longer - just a red biretta. Always hate to see long-standing traditions tossed aside for seemingly no reason.