Good morning Becky,
With that slight droopy eyelid it dose look like Horner's Syndrome. It was probably caused by an ear infection, often a middle or inner ear problem. If his ear drum ruptured then the infection could have entered the ear. Or it could have started in his upper pharynx, where the back of the mouth and throat come together. This area is under the ear, only inside.
With proper antibiotics he may overcome it with time. However it would be a good idea to also check for any polyps in the ear and clean out the debris. Then the ear drum could be checked. This has to be done under anaesthesia.
At the same time, the pharynx could be checked for injury or tumor.
It is a very good sign that he is getting better. Hopefully he will have a full recovery.
As to the voracious appetite. It could be that he has been feral and food was difficult to find. He may have been conditioned to eat fast when food was available. I had a rescued feral cat that did that for a while. I gave him smaller amounts throughout the day and gradually he realized that his food supply was secure and he didn't have to wolf it down.
He should also be checked for diabetes which can increase his appetite without weight gain.
Rechecking his stool and reworming if needed is a good idea.
I'm really pleased to see that he is improving. You are an angel to have taken him in.
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Thank you Becky and have Happy Holidays!!