Night time in the US (especially California) has always been a quieter time. I live in Europe and when I am regularly checking HN I can often tell when it's start of working time in the Bay based on the front page.
You can do a quick analysis but my observation is that stories on the front page during west coast night time are significantly more stale (submitted more hours ago) and/or with less points. Something getting near the top during that time with ~10 points is nothing unusual (especially if the upvotes happen this fast).
Edit: Also moderator intervention is a much more likely hypothesis than 'tricking the system' on average on HN, but this case is well within the norm so I wouldnt suspect that.
If it helps any it was posted just before lunch UK time (which is why I'm here, hello!)
bon appétit
My concern was more of 'Tricking the system?'