Is hyperventilation due to lung problem or neurological problem?

Could be either. Your body is set to breath only as much as you need oxygen or have to rid carbon dioxide. If the lungs become diseased and cannot perform its normal function, the body will respond by causing a higher respiratory minute volume(both rate and depth of breathing). Certain central nervous system problems may cause increased minute volume also, such as heavy alcohol intoxication, high fever.
Can be both. Hyperventilation can be due to both, but usually is due to anxiety ... Some hyperventilation is normal, such as during exercise, when your body is trying to get rid of excess carbon dioxide ...