It depends on how much rest you're getting inbetween your intervals. If the rest is short enough that your heart rate never goes back down to normal, then you're also working your aerobic capacity.

When I train jiu-jitsu, I do several rounds of live rolling. Usually something like 4 6-minute rounds with a minute rest inbetween. The hard part of live rolling is the anaerobic part: quick spurts of high intensity. How fast you can recover from them, and how often you can sustain doing them over time determines how well, athletically, you will do. But this is also a 30 minute period with an elevated heart-rate, and you never are fully rested inbetween your anaerobic bursts. So, it is also an aerobic workout.

Despite not doing much explicit cardio training, I still have the cardio capacity to run decent distances with decent times, on the rare occasions I do. That's because I am training my aerobic system even though most of the exercises are anaerobic. (I once went on a 9 mile run having not gone on a run in over 6 months, having only done jiu-jitsu training and conditioning during that time. My lungs were fine. My legs were not.)

You can run easily because your placate threshold has been significantly increased... doing sprints won't improve your aerobic capacity to any great degree... just ask Usain Bolt

My point is that I am training both, even though my anaerobic capacity is the real determinant of the outcome. But inbetween bursts, I am still active, just at low to moderate levels, and this occurs over a long period of time.

If your sprint workouts involve sprints with very light jogging inbetween then you will work both.

Many people will tell you that when you go in to "sugar burning" (approx 140bpm+) mode then you are doing very little to improve your aerobic capacity... Regardless of your heart rate being lower at certain points. Read about Mark Allen's (Ironman champion) experiences with this. To train your aerobic system you need to start in the aerobic zone and stay there religiously. IMHO