They use Microsoft Playfab to verify purchases done with Crom Coin rather than whatever system Steam and other retailers have for DLCs. Doing a quick search on Playfab, its not nearly as secure as other systems when it is offline and Microsoft even recommends content relying on online verification be disabled when offline.
I would have liked it if they used the similar system as their DLC products. However I’ve played games that have done this on the individual item bases and its an utter mess when stuff is done individually. And apparently the $14.99-19.99 DLC bundles weren’t sustainable, which is obviously unfortunate.