The specific Satoshi filter is that prior to OP_RETURN, data of an unknown content type was rejected from being relayed (i.e. filtered). However, a transaction sent directly to a miner with data of an unknown content type could still be mined... the miner could even call the output an "OP_RETURN" (or any other op code unknown to anyone else) if he wanted to. The difference is, when all the other nodes validate a block containing a transaction with an op code that it doesn't recognize, it just assumes it's unspendable - which was convenient for the introduction of OP_RETURN (also unspendable) since it didn't change node behavior vis a vis block validation (and thus, no chain-split) The net result of OP_RETURN was to allow data of unknown content type to be relayed; and consequently, way more likely to get minded - then when it was previous being 'filtered' (i.e. 'picky') from being relayed in the first place.