Olivia Nuzzi is not know to be the most, uh, objective member of the journalistic profession.
I’ve seen a couple of grazing bullet wounds (which still do a surprising amount of damage) as well as multiple industrial injuries to soft tissue (including one on myself which removed part of a fingertip). Even minor wounds can bleed a lot (and especially head wounds) but even a grazing bullet contact to the ear would leave visible swelling and likely tear off a chunk of material, and a supersonic bullet like a 5.56x45mm round would basically pulp the cartilage in proximity to contact. As described by @Lightnin the damaged area would not grow back completely except on a young child as healing damage to cartilage tends to result in fibrous scar tissue.
My speculation based upon the scenario and post-injury images of the ear is that Donald Trump was struck in the ear by some tiny fragment of shrapnel that has struck the stands behind him—either from the copper jacket of the bullet or material from the stands—moving at subsonic speed which just sliced the surface of the edge of the ear, not doing any significant damage but drawing a few drops of blood that then streamed across his face, making it appear more serious than it actually was. The notion that the Trump campaign could successfully conspire to fake such an event complete with sniper beggars belief, but they certainly knew how to milk the most public response from it.
Stranger