In the mid-17th century, he probably sold them some kind of matchlock, rather than flintlock, which were relatively new at the time and were still rather expensive compared to matchlocks. A matchlock is a type of early firing mechanism that works by lowering a piece smoldering potassium-nitrate-impregnated cordage (the "match") down to the touch-hole in the barrel. They were heavy, and took over a minute to reload. The weapons themselves were probably aquebuses, rather than muskets, which were just beginning to become popular at that time; that said, the distinction between an arquebus and a musket has always been a bit fuzzy. These weapons would be smoothbore firearms, probably about 4-6 feet long and weighing about somewhere around 10-15 pounds. They fired a large, low-velocity spherical projectile, with a caliber of about 0.5-0.75 inches and a muzzle velocity in the general somewhere around 600 ft/sec. This large spherical projectile tended to spin unpredictably, so the smoothbore arquebus/muskets had an accurate range of only about 150 yards, and were essentially useless beyond 300 yards or so.

Hudson himself would have sold matchlocks, as /u/TectonicWafer said, given the timeframe involved. But he was just passing through, and matchlocks were never a huge part of European-Native trade. The gun trade didn't pick up until the introduction of the flintlocks, with the French and the Dutch being the main suppliers in the mid-17th Century. The Dutch were selling guns at the price of twenty beaver skins. By the 1640s, the Haudenosaunee had enough guns that they were re-selling them other Native nations, namely the Mahican at the time, and by 1650, the New Netherlands administration was attempting to curtail the gun trade as quickly as possible.

More information about specific guns and the history of the gun trade at the time can be found in Guns of the Early Frontiers: A History of Firearms from Colonial Times through the Years of the Western Fur Trade.