HIIT is not just multiple reps with heavy weight. That is actually just a small part of it and not entirely necessary. And multiple reps are just more than one. So lifting a few times, 1 - 5 reps of a very heavy weight will build strength. Lifting more than a few times of a lighter weight that one can manage for 6 to 12 reps or more, is when muscle mass is built.

HIIT is a structured workout with quite a few different exercises and movements being performed that focus on getting the heart rate elevated to the upper zone multiple times. HIIT itself is not about building muscle. Though one could put the resistance movements necessary to build big muscles in the sequence of their HIIT program.