Using a Dump Truck in place of a Cargo Ship is impractical, yes. However, both do similar things. Just in different capacity. A Cargo Ship is just a big Dump Truck that "swims".
It is true, Blacksmithing and Welding do different things, but they aren't ENTIRELY different. The practice of Forge Welding comes to mind. Forge Welding is done in Blacksmithing. The Welding Association acknowledges that Forge Welding IS a form of Welding. Welding is the process of combining two metals with or without heat and with or without filler metal. Metal is welded with Pressure and Heat. Heat is created under pressure or from an outside source. Blacksmithing is using heat and pressure to combine two metals into one piece, just without the extra "umph" of an electric current. In fact, Blacksmithing and Welding aren't even that different in the ways they heat metal. A Blacksmith might use a gas forge, one powered with Propane. Welders commonly use a 75/25 gas mixture for MIG or TIG welding.
So, in conclusion, your response is not entirely correct. Yes, Blacksmithing and Welding are different, but one was derived from the other. Hence, they do similar things.