In tcg it has been ruled that Rex, Ride Fur Hire can draw when your opponent draws for turn but it does not work the same way on the client
This is not a bug. Card scripts are based on OCG card text, and the OCG card text explicitly says “If a card is added to your opponent’s hand from your Deck by an effect other than a “Fang Brigade” card, and you control another “Fang Brigade” monster, you can activate this effect; draw 1 card.”.
As such, it will only apply to cards added by card effects, not drawing for turn.
As for the TCG card text, there are cases where due to significant differences in TCG vs OCG card texts, that a separate TCG card is required due to the card working differently based on text in a significant way.
For this card, its possible in the future that a separate such TCG version may be added to the game, but likely wont be soon, as Konami has, as of late, corrected several TCG card text errors, such as with Khaos Starsource Dragon, Exosister Betrayal, and Incredible Ecclesia, and as such, theres a decent chance that this card text error is corrected.