Coincidence?

[HerenIstarion]

I do think it's just a coincidence

On a different trend (going off too)

why would Isildur carry a massive rock from Numenor when surely there were more important things to transport?

Well, within sight of oncoming catastrophe, one carries as much or as little as one can carry away. No knowing what other important things there might have been to better warrant transportation expenditures, it may have been simply considered work of art worth saving