Nah... It's very rare that BOTH will, in fact the only time you will get that is HO, Hitech said in the con podcast files. Listen to 2 of 3 (I think that's the one) it explains collisions pretty well.
Also I believe Hitech mentioned (in the podcast) that the radius for instant kills in collisions is small. Outside of that, if they flutter to the ground, they're fair game. However if they blow up instantly you get the kill. It was probably an instant-explosion in this case. Either that, or he saw he was without wings and ejected immediately (thus giving you the kill).