The price was created, and is given, by the Nobel Foundation, which was set up by Nobel's will to carry out his last wish. If you go to the official page of the Nobel Prize the Prize in Economic Sciences is listed with the other Nobel Prizes. Its not one of the original Nobel Prizes, but claiming its a completely different thing is not true.
The price was created by Sweden's central bank, not the Nobel foundation. It's true that it's now considered a Nobel prize proper for most, but that's not to say that it originally wasn't the economics field leeching on the scientific prestige of Nobel. To be honest, it feels pretty on-brand for it. And fwiw, in Swedish, it's almost always clearly distinguished with a "in memory of Nobel" or similar in the surrounding context.
