Just more desperate hairsplitting by guys with none to spare;
One idea of coupling is where the locomotive is coupled to the tender, with devices called 'couplers' and where the the coupled tender moves exactly the same direction and speed as the loco.
Another, broader vision is the coupling of the loco to the cab, or caboose if you prefer it. The net motions of the loco are indeed manifested at the caboose, albeit with more interesting dynamic behavior when there are 100 intervening cars, some heavy, some empty,... I think that the absence of limiting words such as 'tightly' or 'closely' or 'directly' (or 'With fewer than 100 pages of nearly empty schematics) do leave quite a big claim. While there is nothing directly on the point of your question, this stuff at uspto is a good refresher; the glossary (no definition for 'coupled to'
News 
Market Data 
Discover 
