From the pricing page I linked to[1]:
> There are no charges for outbound data transfer when using a dedicated network connection to the RSTOR network and direct peering is established. These connections are charged separately. To find out more please contact us.
I would imagine for enterprise customers you might either be using direct peering / similar or they're able to charge based upon ballpark bandwidth usage. Otherwise I'm unsure as it does seem quite in line with Wasabi otherwise.
[1]: https://console.rstor.space/pricing