I'm pretty sure that ensuring it sank was on the checklist. They don't want it recovered.
At least one of the early Falcon 9 recovery experiments floated after landing in the Pacific, and SpaceX had to arrange the use of weaponry to sink it.
Do you have a link to this?
Not doubting you exactly, but I've never heard of this and would love to know more; ideally, I'd like to read it myself, or better yet see photos!
I've read both of Eric Berger's books, and I don't recall this particular story being in them, and he had stories of practically everything regarding the first 3-4 SpaceX rocket launches.
I'd love to know how they managed to wrangle up the authorization to live-fire an armed missile, or redirect an active-duty naval vessel to target it with artillery, especially given the tense relationships SpaceX had with the USAF and USN in their early years.