Their account is basically right, but I’ve got some quibbles with it.
Manhattan: I have no clue who Robert Guet is, and the 1609 date is questionable. I presume he was a member of Henry Hudson’s crew, as that was the year that Hudson found the island and the river that bears his name. The OED dates the name Manhattan from 1625 in Dutch, citing J. De Laet’s Nieuwe Wereldt. English usage is in place by 1659. The word is from the presumed Munsee word *mənaháhte:nk, “where one gathers bows.”
Bronx: I have a date of 1641 for Jonas Bronck settling in the region. Bronck’s farm was called Broncksland, but the name died out, surviving only in the name of the Bronx River; and it is for the river which the borough was subsequently name.