trending is based ONLY on the real time traffic speed that the video gets, i bet you caught that video with 700 views right on the first 2-3 hours of the campaign when the visible counter was still behind the real time counter...
and BTW, trending is separated to 90 countries (each had it's own trending list) and then there are sub-categories, i still need to run more tests but i'm sure that the ticket to the trending list is very simple, just to get more VPH (from same country) must be more VPH than the video you want to out-trend it (climb above it in the trending list).