I always found it interesting that Iceland has no indigenous population (like the inuit), prior to Scandinavian and British immigration. Like, what if it's because it is regularly buried in lava or something.
There is some evidence that Irish monks were on Iceland before the Norse: https://en.wikipedia.org/wiki/History_of_Iceland#Irish_monks
Were there another non-European population earlier, they would need to get there by sea. I would expect archeological evidence of sea-worthy ships, which we do for the Norse.
It is a long way from Greenland to Iceland - far greater than the ~35 km from Ellesmere Island to Greenland, which is how we think the Dorset and Thule people got to Greenland. (And that was on the other side of Greenland.)
I also find it fascinating, it's a place where there's no "colonializers" and "colonized"...