I'm glad to read your bird is doing better; that's the news everyone here wants to hear, but I'm also responding to an earlier post of yours. Bear with me on this one.
To answer the question, "how is any of this nuerological?", look back to Eggcessive's and Wyorp Rock's posts. Wry Neck is a symptom of an underlying issue, those underlying issues being things like an injury to the head, genetic trait passed down, vitamin deficiencies, poisoning, metal toxicity, and the like. Crop Impactions, Slow Crop, Doughy Crop are often symptoms of a larger underlying condition too, things like poisoning will disrupt the GI tract, infections in the body cavity can cause swelling that puts pressure on parts of the GI tract restricting food passage, Liver and Heart failure could be at play. Mareks and Newcastles come to mind for me in your case, though you suggest they are not in play.
Other underlying issues could be a genetic predisposition to poor balance, possible genetic defects in neurological development, and/or he may suffer from an ongoing vitamin deficiency. Vitamin E and B-Complex vitamins are essential to good neurological development and functioning. If he's not getting enough (or can't process enough), he improves with treatment, but backslides when the therapeutic is removed.
Since we've dealt with another issue recently, I'll share this: After a recent bout with lead poisoning in one of our birds, I'd recommend a vet visit for your boy. We can speculate online for hours on end about symptoms and treatment avenues, but at the end of the day, only testing is going to tell you what afflicts him. My advice is to find out early via X-rays and Blood Work while time is more on your side.
Last, I would heed Wyorp Rock's advice to keep this bird out of the breeding pool or you risk passing negative traits to the offspring, hindering viability of the breed down the line. If this is something that is not genetic, like maybe bad feed, a short-term poisoning event, etc, then if he recovers you might consider breeding him. At the end of the day, only a vet with diagnostic capability is going to be able to filter this down for you.