I have no idea about Alan's boot.

But calluses form where there is stress. They don't as a rule grow where there
is no pressure.

However, with a person with psoriasis, the psoriasis may activate from any
stressor. I wonder if Alan's healing problem is connected to psoriasis too?

One thing you can consider... poor omega-3 status increases callus and dry skin.
When we started them over 10 yrs ago, I lost all the calluses on my feet (and that was with standing at work 8-14hr days).
You say that Alan doesn't eat fish? Where does he get the essential omega-3's in his diet? We must have them you know from food or supplements if the food is not eaten. Omega-3's are used by the body to form skin, mucus membranes etc. Of the omega-3 family the flax oil it the most useful for the skin. Think about that. I have a thread on vitamin forum all about it.
My husband has psoriasis and he uses both flax oil and fish caps. I also buy foods with them in it. (some eggs now come with Omega-3, and Olivio spread or Smart Balance have them.) His psoriasis is more or less under control with no ointments.

I don't understand how there can be callus when he was not walking on the foot? You need to ask the doctor. I don't think an ortho MD would be working on callus however. Psoriasis patients can turn over skin up to 10 times faster than people without it. So it might be a factor.