It does not necessarily count as public good because a camp ground is not a good method of showing importance of the national park as the park is open to the public and should be respected in any means possible as they are open to the public and having it as a campground is not a way of showing its importance.
I'm assuming here that "a public good" refers to a public commodity not owned by a private institution. For this question a campground does not necessarily have to be considered a public good because it can be bought. Campgrounds in national parks can actually be owned by private institutions even though the national park itself is a public good. This means that the national park is a public good but once you step into the campsite, you will be in the property of the owner.
