It was a par 5 throughout the "one division, one champion" phase of the event when there were plenty of players in the event who were not at all Open caliber. Those players were more likely to struggle to reach that sidewalk, and probably dumped down the hill further left to ensure they got in bounds, leaving themselves far too short on the fairway to realistically make the green in three. It was probably those folks that drove the average on the hole up enough to warrant calling it a par 5. So in that sense, the design of the hole warranted calling it par 5. If those players played this hole, there'd be no need to dump short and left anymore and might increase their chances of reaching the green in three for a reasonable chance at a 4.
With the splitting of the tournament into two flights, the Open flight got a lot more elite and the number of players who struggle to make that sidewalk probably shrunk to zero. That's likely why they did away with it in the design...it wasn't affecting scoring at all. So by paring the dead weight from the field, the average dropped and so did the par.
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