However what all these articles forget is that before Columbus, before the Vikings, before the Irish (i will play along and treat include that 'theory' here), before the Chinese (another questionable 'theory' that i will also include just to be fair) .....before all these groups arrived the Native Americans had been here for centuries!
They had crossed eons ago when there was a landbridge (before tectonic shifts and rising waters sealed it off). Hence it was not the Vikings nor the Chinese nor the Spaniards nor the Irish (????) who got here first but the Native Americans.
However if you think of it people have claimed to have been 'the first to see' a valley in the Himalayas (when there was a tribe of Sherpas farming in it), or discover a river in africa (oblivious to the natives fishing in the river), or a lost temple complex in India (apparently ignorant of the fact that for the 'lost' temple to exist someone must have built the darn thing). Mountain ranges (that have villages at their base) have had explorers claim to the the 'first to see' them, probably because somehow the people who had farmed the volcanic slopes for generations apparently had never had the sudden epiphany that they were living next to a mountain!
Hence if that is possible then i guess the Native Americans who had been in N. America for centuries did not factor.