Sometimes fossils are from animals buried in land slides, meteor strikes, etc., but either way I think a “fossil” has to be much older...thousands of years or more. Civ, is 5,000 years enough time to fossilize stuff?
Fossilization is rare; generally it preserves (the shape of) just a small part of an organism, and the rest rots away in short order; anything large, like those fossils of tree trunks which are vertical and penetrate multiple coal seams, clearly had to have been buried (even horizontally) immediately and in entire, in order to be so thoroughly preserved (and minus their limbs and branches), because if part were buried and the rest exposed for up to millions of years, obviously only the small part would have survived (which is much more common).
This particular find of fossils merely shows that a tsunami churned up a bunch of older strata, unearthing existing fossils. This is how the researchers figured out that a tsunami came through. :’)