Despite the differences, it acts roughly like a coinjoin, but it is actually much better. That said, another proof that the supply is not verifiable is that we cannot perform sidechains such as Liquid with Monero's characteristics, nor drivechains (if we could) with Monero's characteristics, because we could not guarantee that 1 BTC = 1 BTC in the sidechain or drivechain; the relationship could be broken at any time.