No, if you pay $1 one time, you’re paying a one time license fee. Not a royalty. A royalty by definition(including your definition) is when a fee is applied based in number of units sold or released(sometimes time limited).
Things can, and often do, have a licensing fee, but not a royalty fee, and saying they’re royalty free is accurate.
It’s not misleading at all, but I’d agree that a good number of people don’t know what a royalty is.