IIUC Narwhal 1 will be free but will drop its ads in return for being free (so a non-commercial app). Rather than a special deal I figure that this passed under the same rule that other noncommercial apps like RedReader did.
Narwhal 2 will charge a subscription to cover the API fees, including top up fees if you go over some limit, suggesting this is the normal reddit API pricing. I think developers of like Apollo couldn't do this because they had preexisting annual subscriptions. I guess Narwhal didn't have anything like this.