” and I doubt that he swam back to Edgartown.”
Why do you doubt that?
.
The only evidence that he swam the channel is his own self-serving say-so.
But it was dark. I'm not sure that swimming that channel is easy. I'm not sure anyone has seen Kennedy swimming any time since either. (Google for images: Ted Kennedy swimming) I don't believe anyone has said that they saw him in wet clothes in Edgartown, including the clerk at the Edgartown Inn where he apparently awoke in the morning.
ML/NJ