Vikings had discovered the American continent centuries before 1492, the year of Columbus' trip. How did the information about the huge discovery got lost? It would not have seemed surprising to me if Columbus had some knowledge of Viking expeditions, but he really believed to have visited Asia instead.
Simply, the Greenland settlement those discoveries were centered on died out before the Printing Press. The last anyone heard from it for sure was 1410, and Gutenberg started working on his press in 1436.
Back then information had to be hand-copied by professional scribes, which was a relatively time-consuming and expensive process. Because of this, only the most valuable of information would get copied and disseminated widely, and then generally only to people who really needed or strongly desired to know it.
A few dozen Icelanders finding some new frozen land way up north they could barely survive in just wasn't a concern to most people. The only evidence I've seen that anyone outside of the Norse community was even aware of Greenland's existence is the paperwork the Church had to periodically send around when the settlement needed a new Priest, or couldn't send it tithes because it was so poverty-stricken. Its quite possible the Church hierarchy had no real conception of where Greenland was, other than that they periodically had to send a priest to Denmark so that people who did know where it was could get him there.
There's very little indication anyone else in the Mediterranean area had ever heard of the place. It doesn't show up on any of the early maps created by the Iberian or Italian maritime community that was performing most of the work of exploring new ways to get to the Indies.
Conversely, when Columbus came back from his explorations, his findings could be easily and cheaply reproduced and disseminated throughout Europe due to its printing presses, which informed the entire continent about it, and allowed its greatest minds to ponder the true significance of what was being found.