Yes. But it is not high intensity interval training (HIIT). In HIIT, the work segment is so strenuous that you cannot do it for longer than 30 seconds.
So if you find that you can keep stepping onto that box for longer than 30 seconds, this is not HIIT. If you can keep doing this for longer than a few minutes, it’s not even general interval training.
The interval should be challenging enough such that it cannot be sustained for longer than a few minutes.
So in the case of a stepping stool or box, something must be modified to bring on high fatigue. You must know how to tweak your program to impose a high demand on your body.
In the case of stepping, a higher stepping surface will increase intensity. Other ways to increase intensity include: faster stepping speed, adding a jump to every step, adding a squat every time you step onto the box, or adding a squat jump every time you step onto the box.