It's not just the fact that the area was covered by ice. The local geology is also a factor.

Glacial erratics are everywhere in Scandinavia, which also obviously was covered by the ice. Small ones, like in the article, are scattered all over. Large ones weigh thousands of tons and may often be mistaken for bedrock.

I suspect there are other areas in North America where that's also true.

There are no mountains in Ontario or Saskatchewan and that is where the glaciers came from, there’s only the exposed bedrock of the Canadian Shield.

Glacial erratic https://en.wikipedia.org/wiki/Glacial_erratic