While I agree with your list of Viking accomplishments, I would be willing to bet that the ships that were used in those endeavours were significantly larger than the one in this article.
At about 50 ft long and about 8 ft wide this was no cargo and people transport. It is a fast, short range troop transport or possibly a ferry of some sort. Depending on the availability of labor, construction time was probably a few weeks if that.
They had different standards. Back when ships were 100% made out of wood, long trips were accomplished using watercraft we wouldn’t use to cross a creek.