Yes, it is perfectly normal! The white portion of his bowel movement is actually urates, which is the bearded dragon version of urine.
Because, in the wild, beardies don't really live in areas that have a lot of water, their kidneys have evolved, over the years, to be able to extract nearly every bit of moisture that their bodies take in. What is filtered out by the kidneys, therefore, is expelled as a white, chalky like, powder, rather than liquid urine!
Also, just as a point of note, if you ever notice that the white portion of your beardie's bowel movements are being expelled in a hard lump, rather than in powder form, that is one of the first signs that your beardie is becoming dehydrated, and is not taking in enough moisture These lumps are called urate plugs, and can sometimes be very difficult for them to pass, so if you notice this happening, make sure that you get more water into him! If your beardie refuses to drink for you, you can always give him a good soak in warm water for 20-30 minute to rehydrate him. Bearded dragons have the ability to absorb a certain amount of water through their vents, so giving them a 20-30 minute
bath is an excellent way to make sure that they stay well
hydrated!