There were a lot of reports many hours before the russians acknowledged anything that the Ukrainians did it. From many different sources. Then there was the SOS captured by hundreds of regular users on the websdr source. Also, there was a captured conversion by the russian military discussing how it was done – Bayraktar took out the ship's radar and took attention away from the missiles that were launched from the shore.

Everything fits, there's no reason to believe russian propaganda now. They are just trying to save their non-existent face.