Artifacts that survive this long are usually found in a buried context, which can, under favorable conditions, preserve them for long periods of time.

The artifact can be buried by colluvial(gravity driven), or alluvial(water driven) deposition before they have a chance to decay. For more information you can consult a geomorphologist, which I am not.

I have the same question - My guess is at that altitude, temperature, and under an ice sheet, and silt until the lake was drained. Here's the paper: https://www.cambridge.org/core/journals/antiquity/article/in...

Intact human bodies thousands of years old have been found in Irish bogs - cold, anoxic, acidic. Apparently in this case cold and anoxic were part of it, and also pine resin in the wood acting as a perservative.

Likely isolated from oxygen in deep water or sediment

In the peat bogs on Skye where I grew up and where people still cut peat for fuel, you often see the remains of silver birch trees that must have grown a couple of thousand years ago.

They're often so well-preserved that not only can you clearly see the markings on the bark but you can sometimes make out the rings in the wood.

I remember my dad pulling out a piece that was so well preserved you could see where deer had gnawed it.