The headstone is probably more than enough; we understand the Ancestors had some sort of conception of death and possibly an afterlife because neolithic and even Neanderthals were buried, often with flowers or rubbed with red ocher or other dyes.
A typical modern human burial (at least in the West, as implied by the OP), would have the body preserved with formaldehyde, the skin prepared with makeup, the body dressed in a suit or similar clothing and then laid in a casket made of wood or metal, with metal fittings such as hinges, clasps, carrying handles etc. The casket is lowered in an artificially dug hole (traditionally 6'X4'X6' deep).
So the archeologists would discover:
A cut headstone, with indecipherable but fairly obviously artificial carvings on it. The stone itself may have marks on it left by mechanical saws used to cut it to size, or the polishing process. The stone is not simply set in the ground, it may be resting on a footer or foundation of some sort. Edit to add, based on some comments, the stone itself is unlikely to be native to the area where it was found, and even badly eroded would be an odd shape and size given the local geology of the region.
A headstone on a base
An obviously dug hole. The earth in the hole does not match the layering of the earth outside of the hole, but seems to have been randomly backfilled. This is even more obvious given the implication by the OP that the entire cemetery site has been buried for two millennia, there are distinct layerings of earth over top of the site as well.
natural layers of soil
The remains of the casket. The wood would leave fairly obvious residue in the ground, and a metal casket would be corroded but may possibly be recognizable depending on the material and conditions of burial. The metal fittings would be fairly obviously artificial as well. Current technologies would allow the archaeologist to date the remains of the wooden casket, and a good guess as to the age of the burial could be made by examining the metal, corrosion and so on.
A casket showing the multitude of fittings and liner that will become evidence in the ground
The body would likely have decomposed, but there would be interesting residues on the bones from the chemicals used to preserve the body, cosmetics, the decayed clothing and shoe leather, the lining of the casket and so on. It is possible that some of the materials (especially synthetics) night even have been preserved over this time. A skeleton with rayon socks and underwear would be a bit difficult to explain otherwise.
So the future archaeologists would not wonder for very long if the burial was "artificial", nor would they be in doubt about the ability of these long ago people to create and use technology. As an aside, considering we can read many "dead" languages from civilizations as far back as the Bronze age (Sanskrit, Hittite, Linear B, Egyptian hieroglyphs etc.), it seems a bit strange that they cannot read or decipher our languages. A well preserved plaque on the Moon on the side of the Apollo LEM's would provide a great way to begin studying English, for example.
LEM plaque. The LEM itself will be recognizable for a quarter billion years, the plaque should be good for a million or so