When the grave was dug, one of the urns inside was turned upside down, one fell over, and the other was out of position.

It’s not surprising or superstitious. The most reasonable explanation is water. When there is a lot of rain or even flooding, more water seeps into the tomb. The mouth of the tomb is closed and the water is not easy to drain out. It accumulates. If there is too much water, the urn will float, causing the urn to tilt or stand upside down. Another factor in the inversion is that there is a lid on the top of the urn, and some sealing materials such as cement are relatively heavy. This causes the top of the urn to be heavier than the bottom, and it is easy to invert once it floats.