I’ve believed this to be a turnover too, though I’m questioning that now as it definitely doesn’t seem fair and does not “simulate what would most likely have occurred had there been no breach”.
Could be that that there was no obstruction at the time of the throw so handler didn’t call it; or worse, the non-player was on the opposite team (bad spirit or unintentional obstruction, but still worse than a spectator affecting play).
Rules “decision diagram” would be something like this:
Play obstructed – yes.
Within 3m – yes.
Then, the obstructed player can call Violation.
Thanks for the response, Benji, – still trying to see if there’s a convention we all follow here which isn’t in line with the rules.