This is the usual way of dating buried archaeological finds - you work out when the thing was buried by studying the surrounding material. In this case the specific dating technique is new, but the principle is well established. If you find something buried in material that was laid down 470,000 years ago, then the thing was buried at that time. Assuming teleportation doesn't exist, how else could the artefacts get there? The only other option I can think of is deliberate burial and I imagine archaeologists would already have considered that idea.

As to finding and using extremely old wood - wood does not survive that long except in cases of very specific environmental conditions like this one; surely another reason to expect that the wood has lain undisturbed for its entire history, rather than having been dug up and turned into some structure a few thousand years ago (then buried again).