Nah, nothing special there. The #731 is from the Sun/Moon Dex, while #765 is the number Oranguru sits at on the National Dex. If you look at the bottom left of the card, you should see more numbers about the card itself and not the Pokémon on it. It should read: 114/156.
On that note though, many cards are reprinted time and time again, being put into different sets or exclusive releases, and all of them have different corresponding numbers on the bottom. So you may see duplicates like that in the future! :)