It's a 1700 parallel twin not a V twin. So it's hardly a copy. Don't see how you can make a cruiser any other way. It might be an American style but it's not exclusively a Harley style. So it's a black cruiser style bike and aimed at the same market sector.
That's like saying every bike with a full fairing is a copy of the BMW R100RS, while intrinsically there are similarities in all bikes with full fairings due to function the bike is built to carry out you could hardly sat they were all copies of it.
All the American motorcycles developed along the same lines which no doubt had a lot to do with the types of roads they were used on. At one time Harley didn't make bikes like the fat bob.
Wikipedia says:
"The bobber was the earliest custom motorcycle built by individuals with mechanical skills and often part of the early biker clubs scene before there were any such thing as a choppers, a simple stripped down motorcycle . It is a style of custom motorcycle which took shape in the 1940s and 50s , generally thought to have been started by returning WW II servicemen working on ex-military motorcycles and inspired by lighter European motorcycles they had seen and ridden.
The bikes reflected their owners and were often homemade but today there are many companies that create such vehicles The style has also influenced motorcycle manufacturers such as Harley Davison."
So in fact the Fat bob design is influenced by home made attempts to copy European bikes (like the Triumph twins) and hence the Fat Bob is in many ways a copy of a Triumph.
So it strikes me as ironic that you accuse Triumph of copying a bike that is in fact a copy of a Triumph
It's a funny old world