To be fair, this is a mistake that started with the Google paper, and everyone else just copies the mistake.
The paper calls them Macaroons as a play on (browser) Cookies with layers (of caveats) - so clearly they meant macarons as well, since a macaroon doesn't have layers. Or at least, that's always been my interpretation of the name. It's possible it was just an arbitrary play on hMAC cookies and not the layers?
I had that thought, although according to another comment the definitions have crossover. Probably because people so frequently confuse the two, but here we are.
Macaroon: https://en.wikipedia.org/wiki/Macaroon Macaron: https://en.wikipedia.org/wiki/Macaron