the dragon scale refers to the irridescent body pattern on the body. normally you will see the middle part of the bodie irredescent and the outside not. Your vieltail looks like he has some pinappleing in him which is the black etch to the scales. Another word of advice, betta splendens is the species with all the different morphs in them. Sometimes morphs are crossed and you can see multiple traits in them. I wouldn't call this betta a dragon scale because of the lack of scaling.
Dragonscale is a more pronounced looking thicker scale (so you are going to be able to see each individual scale on the fish and some of the time it is outlined lightly in another color, most of the time black).
You have a pretty delta male, his tail should grow out some more with care.
Edit: Pineapple is a dark outlined scale pattern, kind of like a pineapple that isn't quite ripe.