So i emailed pdga and this was their response.
First of all, props for being such an even-keeled person. Many players would have had a fit.
There's no obvious answer for this situation. Obviously, it would have been better if the player on your left had been paying
more attention. He could possibly have been given a courtesy warning for playing out of turn, but that wouldn't have helped you.
It also doesn't*quite fit into the interference rules, as it's hard to call it intentional (as in malicious) interference, which would result in a
re-throw for you. You also bear some responsibility for not noticing that someone else may have been intending to putt out.
(When I'm putting out, I usually make eye contact with anyone else who may be putting out at the same time.)
So, given the rules as they are now, I think it falls under "**** happens", and again I commend you for*your equanimity.