Okay a bitcoin transaction can be used to ferry a small amount of information around. Max 80 bytes. The specific way this is achieved is by using an operation in the spend script called OP_RETURN.

OP_RETURN has been highly controversial in days of Bitcoin yore, and before a cap was imposes, people used it to stick larger amounts of arbitrary data in transactions.

The OCEAN mining pool is coordinated by Luke's own alternative node implementation called Knots. Knots basically is Bitcoin Core with some feature patches and different default values applied. One of those different default values is 40-something bytes for OP_RETURN data. Why? Because Luke probably disagreed back in the day with 80 bytes in Core.

Samourai maintains Whirlpool, a non-custodial mixing service. Whirlpool generates transactions that utilize OP_RETURN to carry around some information about the mix round. That information exceeds Knots' max threshold, therefore those transactions never appear in block templates to the miners.

I think that's that gist of it.