I believe that if you or your wife were not US citizens at the time of your child's birth, your child would be entitled to ROA (right of abode). The exception is if your child was born before 1997 and your child has returned to HK before 2000 to establish ROA.
Being in HK for 90 days in a year would not count as being ordinarily resident. Immigration has records of entry and departure and would easily have access to this information.