At least in Brazil, it's not considered truly the Amazon until the Rio Solimões and Rio Negro combine, which makes sense, as they are the two enormous tributaries that combine to form the mega-river. You're splitting hairs here, of course the tributaries have bridges across them.

That said I do agree that the whole premise of the article is pretty dumb, considering the Brazilians fairly easily (minus graft) built a bridge across the Rio Negro right before it becomes the Amazon. If they wanted to, they could do it after as well.