Good question. I haven't gone as far as seeing if a specific flight has a different price or not. It is, however, from the same airline that Hipmunk has a lower price for. I do know that. I'm not sure if it's the same specific flight or not, though. I can look into it more...

In general, I based my original comment on what Google Flights show as the "Best Price" vs what Hipmunk is showing as "Best Price." And there isn't any filters on either platform that would be quick to explain why the huge price difference.