Here's how I understand it, and nostr:npub1wnlu28xrq9gv77dkevck6ws4euej4v568rlvn66gf2c428tdrptqq3n3wr can correct me if I have anything incorrect.

Pool-mining normally requires the pool to create the block templates using their node, which are sent out to the miners on the pool to hash. Any block found is then sent to the pool and broadcast out to the network using their node. The template they send to the miners does not include any kind of reward split, because ALL of the rewards goes to the pool, and they internally credit sats to each miner's account, after taking their fee.

DATUM changed this whole dynamic. Miners on nostr:npub1qtvl2em0llpnnllffhat8zltugwwz97x79gfmxfz4qk52n6zpk3qq87dze that are using DATUM are not getting a block template from the pool at all. They are connecting their miners to their own Bitcoin full-nodes to get block templates to hash, and if their miner finds a block, their own node will broadcast that block to the network. As such, they are solo-mining, since there is no need to send the block to the pool for it to be broadcast using the pool's node.

The only thing that DATUM requests from OCEAN is a reward split. This is entirely voluntary, though. They could just give themselves the entire reward. However, this means that OCEAN would exclude them from the reward splits that other miners are including in their block templates. OCEAN knows how much should go to each miner because DATUM sends OCEAN the valid shares they produced. Part of those shares being considered valid by OCEAN is that they are using the reward splits provided to them, rather than lottery mining by only paying themselves the reward from any block they might find.