Could be, but I didn’t find anything else coming in from the pacific at that moment. I only noticed it because it came into the area from the west alone and was very conspicuous, but it did pass overhead as it arrived from the ocean so the arcraft did arrive.
This happened again just now (7:35pm pacific) with SIA2, a Singapore Airlines 747, which normally flies between Hong Kong and SFO. Very loud as it passed overhead, so I believe it likely was a 744. The arrival time is correct as well based on previous flights, but no record of it since October on the list, (and no other flight on the list which coud be it under a different number.)
So far all the flights I have noticed missing from the list were arriving at SFO or OAK from the ocean, which could be a clue. Perhaps when they are picked up in the system in mid-flight something is bouncing them out of the list. Could it be an effect of the dateline?