Just a thought here..
NPCs and players use exactly the same flight model - this has been confirmed by Sarah multiple times, that all the AI logic does is provide control inputs. As a player, I can confirm that when my thrusters were shot out my ship maintained its velocity AND its angular velocity - If I was moving in a straight line I'd stay straight and not tumble, if I was turning I'd be tumbling. Losing my thrusters had exactly the same effect on my flight path as turning off FA, zeroing the throttle and letting go of the controls.
We know Sarah has been working real hard on making the NPCs "better pilots" and one of the things she's mentioned is they are making greater use of FA-off flight. Perhaps we're seeing a greater incidence of NPCs tumbling and receding at a high speed because it's just more likely that at the moment their thrusters were destroyed they were frantically dodging while FA-off boosting, just like you or I would be doing if somebody was shooting up our tails?