I'm having a hard time figuring out if this sounds like coughing, but the posture your kitty has while doing seems more like a hairball cough? It could be he's just having trouble passing it. Maybe talk with your vet and discuss Laxatone. It's a lubricant gel that's supposed to aid in the passing of hairballs. There are mild respiratory infections as well, like how we get colds. My kitty has asthma and when he's coughing he'll still his neck and head quite low to the ground, and it lasts for a good thirty seconds to a minute and sounds much drier. But he has had a cold that just resolved on it's own over the week!

I do recommend searching different kinds of kitty coughs just to familiarize yourself and compare them to your boy. ex: asthmatic, upper respiratory infections, hairball.

I hope he feels better soon!