Sometimes HN admins revive quality posts that didn't get much traction when they were first posted. When this happens, the timestamps are updated to make the post look new.
I can't say for sure whether this is what happened here, but it is a possible explanation.
eddyg|1 month ago
(For more details on posts getting “rescued”, see Dan’s comment here: https://news.ycombinator.com/item?id=11662380)