I broke my foot about 18 months ago, and it was really weird when I tried to walk. II would wear my boot during the day and take it off in the evening. Little by little I trusted my foot more, and I didn't really know HOW to walk. I know that sounds strange, but I really had to try hard not to think too much about it and just let my foot do it's thing.
The walking boot was great for me, because it really took the pressure off of the part of my foot that I broke. But it kept my foot in a flexed position, where the toe was higher in the air than the heel. It also kept my heel a couple of inches off the ground. There's no way for him to walk "normal" while wearing the boot.
One thing that did help me was walking around and moving around in the swimming pool. I have a membership at the YMCA, so I went to the pool there as often as I could just to move around and work my muscles in an environment where I felt safe.
Another thing I did was move my foot around as much as I could while sitting on the couch or lying in bed. Any movement (where he isn't afraid of falling or putting too much pressure on his leg) is going to help those muscles.
I don't think you're helping him at all by telling him to try to walk normal. He likely is trying to do that and is trying to figure out what that is.