Confused by Dimmer Wiring

I have a light on a dimmer that flickers so I was going to remove the dimmer and put a regular single pole switch. I've changed switches before so I'm familiar with changing switches when the power goes to the switch or the power goes to the light. I was a bit confused by what's going on when I turned off the power, opened the switch and saw the following (image included):

Two 14/2 cables coming into switch box:

1. Two blacks from both cables are twisted together with yellow nut
2. Two grounds from both cables are twisted together. The first red from the dimmer is taped to the grounds (behind the orange nut on the left)
3. The second red coming from dimmer is unused and still has the sticker saying not to remove.
4. White from one cable is twisted to black from dimmer (orange nut on right)
5. White from other cable is twisted to green from dimmer (orange nut on left)

One 14/2 cable coming into the light fixture:

1. Black wire from cable attached to black wire on light fixture
2. White wire from cable attached to white wire on light fixture

Thanks for any help figuring this out!