Could Westbrook play the 2 guard just as easily as he could the point? Yes he could. Therefore: combo guard.
That isn't the definition of a combo guard to me. Any PG who is above 6'3 can play the 2 guard most times.
I see combo guard referred to more as a SG who is either 1.) Too small to be a SG or 2.)Is very ball dominant and does not have great vision/passing ability/willingness
Westbrook averaged 8 APG during his 2nd and 3rd years in the league, he is down to 5.5 this year, but I think having 8 APG in your 2nd year is enough for you to be considered a PG.