SAN-HNL is indeed planned to go to the 321. I suspect there's more to this story however. IMO, something had to switch to the 321 to free up a plane for the 3rd daily HND flight. SAN was the next logical move. Perhaps HAL sees seasonality opportunities with the 330 in SAN in the future. I don't think this move is as cut and dry as it appears.
Bummer for SAN, at least for the time being... big downgauge.