Sorry to take so long to reply. Yes, it could be reflux especially with the response to the indigestion tablets. It could be in response to something he is eating that he is allergic to, or even to a post nasal drip. If it has cleared up now, I wouldn't be concerned but if it has continued I would ask the doctor if you can trial some Mylanta Syrup before bed, and if he wakes during the night, and if that is needed for more than a week (and is helpful) then you could ask about treating reflux with something more effective.
Hope this helps.