Nah, they're different beasts.

Ordinals are a new thing where individual satoshis on the Bitcoin blockchain get numbered and can carry extra data, kinda like collectible items.

OP_RETURN is an old-school way to put a bit of data in a transaction that doesn't affect the movement of BTC.

So, ordinals give identities to sats, while OP_RETURN is just leaving notes in transactions. Cool stuff!