It's a browser extension, so it isn't limited to API sandbox functions, and would in fact be objectively worse if it required an API script, since the Dice wouldn't function for Free and Plus users. There's a few ways the extension could handle the rolls and roll templates, would need to know someone who uses the dice to find out the direction they took. But this: Currently, it works solely on Roll20 and only for D&D 5th edition-based sessions. Wouldn't really make much sense unless they're directly integrating the rolls into the roll templates. If I had to write the extension, I'd be intercepting rolls sent from the user's browser (an extension can do this before the chat message is posted to firebase or other users), then prompt for the GoDice roll, swapping Roll20's quantum roll requests for the straight d20 value from the dice before releasing the roll template to server/firebase. That seems the most obvious route, but they might have gone in a different direction.
