On the photo you see a violation of rules listed as one of the reasons this commit is made. Because it’s at the top the meme creator is presuming that’s their main priority.
And they disagree with that, so they’re calling them a “park ranger”. I’m guessing they’re alluding to an old but common media presentation of park rangers being childish about rules.
I get the joke with that it looks a bit odd to put that reason at the top of the list, but their response I find more unkind than funny