Columbus was neither the first human to discover the Americas, nor was he the first European.
In particular, the Aleutian Island chain is no real barrier to natives in possession of simple boats. The Aleut peoples to this day live on both sides, using little more technology than was available 20,000 years ago. The linguistic and genetic evidence we have seems to show there were at least three waves of immigration through that area, two of which while there was no land-bridge.
What Columbus was first at was he was the first person from a society that possessed printing presses to discover the Americas. Gutenberg's first press was operational by 1439, but it wasn't until the late 1400's that printing really started to spread all over Europe. Columbus' discovery was of course in 1492.
This was important because it meant that the knowledge of this discovery could be efficiently mass-produced and disseminated throughout the literate world.