House Cannith is one of the dragonmarked houses. They bear the Mark of Making; their dragonmark aids in the creation of both mundane and magical devices. They are the undisputed leaders of manufacture and trade throughout Khorvaire, and even independent artisans and artificers often study at House Cannith institutions and adhere to House Cannith standards. The warforged, the lightning rail, and the magical lights that line Sharn's streets were all created by House Cannith. It has always been the richest house, but the Last War made it far richer, as every nation wanted weapons, armour, vehicles, tools - and, of course, warforged. Even the destruction of House Cannith's headquarters and the death of its patriarch and his heir in the Day of Mourning did not shake its position as the wealthiest and most politically powerful house, but now three factions wrestle for control of the House - Cannith East, located in Karrnath and led by Zorlan d'Cannith; Cannith West, located in Aundair and led by Jorlanna d'Cannith; and Cannith South, located in Breland and led by the young but brilliant Merrix d'Cannith.
Rolin's disbelief that House Cannith could create something that "doesn't even work right" is probably a bit overblown. House Cannith is considered the leader in manufacturing, but they still make mistakes - they're still human, after all. Nonetheless, if they sold a prosthetic limb that occasionally went rogue and started groping random bystanders, that would definitely be an embarrassment and a black mark on any House member's reputation.
Crow hasn't heard the name "Eugene d'Cannith" before, but that's not necessarily strange. Every House is a large, sprawling clan, and not everyone associated with the House is a big deal. The prefix "d'" indicates that Eugene d'Cannith has manifested his dragonmark, which means he has access to its magical powers. This is true for about half of all House members.
Before, Crow had noticed that the prosthetic limbs are very similar in construction to warforged physiology. If they came from House Cannith, then it is very possible that they were actually created using the creation forges, which were used to create the warforged themselves. However, the Treaty of Thronehold, which declared the end of the Last War, also prohibited the creation of more warforged, and all creation forges were, officially, dismantled.