Why do some think Greg and Amethyst used to date in Maximum capacity when it was obvious that they just used to be friends?

I was always confused by this since it was obvious that Amethyst clearly resented Greg for taking Rose away from her by saying "I had someone who was always there for me until she started hanging out with you!" and when she turned into Rose. It was even conformed by Matt Burnett when he said Amethyst was lashing out to just mess with Greg.

Where did this come from and why do people keep saying they dated?