This could be so many things and since I don't know the nature of your disability and I have no medical experience whatsoever, I'm just gonna spit some bro-science to up my post count.
a) Maybe working out strengthened the muscles around the area you had the disability in therefore reducing the shaking. This is pretty unlikely though since 3 days isn't enough to see that effect.
b) Maybe working out stimulated growth of new neural pathways and improved older ones thus counteracting the effect your disability had on your hands. This is again not that likely imo though since it's only been 3 days.
c) The most likely thing imo is either placebo or just you being so tired/sore that you don't notice the hand shaking.
Exercise is great and fixes alot of problems caused by living a sedentary lifestyle, but 3 days just isn't enough time to see these effects tbh... Keep working out though lol