Children can awaken for other reasons. Occasionally a child may have airway obstruction and resultant sleep apnea as the cause. Such children tend to snore, hold their breath during sleep, and are unusually drowsy during the day. Your son seems to be going to bed at an appropriate time. However, he may still need his afternoon nap.
Children often do until about age four.
I am uncertain why this was eliminated. Perhaps at least a quiet time could be reinstituted for him in the afternoon and you could see what effect, if any, this has on his night time sleep pattern. Having a separate bedroom at night, if he does not have one, could help by facilitating the attenuation of sound, once you are assured of his otherwise good health. Such a sleeping arrangement may not be possible in your circumstances. Parasomnias include night terrors, sleep walking, and sleep talking.