The idea of "discovery," in this sort of context at least, is inherently euro-centric. Columbus initially got credit for the "discovery" because his arrival in the Americas was the most important from a European perspective. Once it became apparent that other Europeans had reached the Americas first, and even managed to write down an account of their discovery (though news didn't spread very far), there was a push to credit the Norse as the discoverers of America. The non-European people already living there are usually left out of the discovery equation.

On one hand, this is because crediting a European explorer for the discovery, aids European imperialist powers in their land claims, citing what's known today as the Discovery Doctrine - the idea that whichever power discovers a land gets to lay claim to it. This is why the English, when they were first eyeing North America for its colonial potential in the late-1500s, started promoting the notion that the Welsh prince Madoc was had reached the Americas before Columbus.

On the other hand, multiple people can discover the same thing. Mathematicians in Mesoamerica and India both get credit for discovering / inventing the concept of zero, for example. So Lief Ericson and Christopher Columbus get the credit for discovering the Americas for Europeans, while some unknown ancestor of the Inuit, Yupik, and Aleut get the credit for discovering the Americas for them before that. And some unknown ancestor of the Athabaskans gets the credit for discovering the Americas before that. And some unknown Paleoindian person gets the credit for being the very first person to enter the Americas.

A small correction, though, to your initial question. The Inuit didn't travel to the Americas in 1000 CE. The Inuit expansion eastward around that time began in northern Alaska, but their ancestors had crossed over the Bering Strait about 3500 years earlier. The Inuit and Inupiat peoples had little contact back across the strait, but their Yupik relatives in southeastern Alaska made regular trips back and forth (with a few recent interruptions due to restrictions placed on them by US and Russia).