At least from that camera angle, looks like it was maybe a comeback route that wasn’t open? Or it wasn’t a comeback route at all and Williams threw it way behind him.
hard to tell from that angle. it looks like a comeback route against press man coverage. if the corner has saftey help over the top he wouldn’t be too concerned with getting beat deep, making a comeback less effective. its possible the QB should have never thrown there tho, and that the WR wasn’t expecting it to be thrown