Looking at the images in the article, I think c), d) and e) in the first group, and the close-up image a couple of paragraphs later, are all the same item.

So. e) looks like d) with a top covering taken off. And, from the curved "handles" visible in c), e) and the close-up, they could all be the same glass vessel. We can see in c) that the vessel does have a lid. In e) and the close-up, there appears to be a residue where the lid rested against the container.

So it's possible that liquid from the jar got to the join, evaporated, and left behind a substance that sealed the container against further evaporation?

You'd probably have to read the full report for an actual explanation, but that's my guess from what's reported in the linked article itself.