Campsite etiquette?

Staying at Meteor Crater RV Park in AZ. In the electric/water only section (no sewer). Came out of the R-Pod this morning to see the camper next to me draining their gray tank directly onto the gravel.

Relieved it's not the black tank! But I can't believe this is good campground etiquette. Am I overreacting?

I would be concerned about any residue left from the last time the black water tank was drained.

If the shower drains into the gray water tank, then there is a danger of e. coli being spread, among other diseases.  Since the gray and black water drain converge in the drain outlet, it is really impossible to drain the gray water without washing out black tank residue with it, including e. coli, unless you scrub the drain Y with bleach or other disinfectant.  It's not a good idea to drain that sort of thing into a camp ground and in most places is illegal. 

I don't think you are overreacting. Bad etiquette - YES! Possibly/probably contrary to Park rules.

Personally, I don't want to walk and live in anybody's waste water. Even campgrounds without hookups or dump stations usually have some provision for the disposal of gray water (dishwashing, etc.).

I have words that I use to describe folks who do this but, they are not suitable for the fine folks here on the forum.

Looks like a combo drain as used in van campers. On the left is the black drain valve, it is closed on right is the gray drain which is open, I can see the stem. One drain hook-up for hose. The pic shows it is not a travel trailer.