See the white hairs around the top of the tail those are guard hairs. It can make it look like the dorsal goes down the the tail when the horse is older as the white guard hairs lengthen as the horse gets older.
There is a photo of a bay Arabian that has incrediably convicing leg barring and a dorsal stripe. As both the dun and cream genes are non-existant in purered Arabians, it is obviously due to counter shading.
I would say testing is the only way to be sure on this boy without knowing his lineage. Posted via Mobile Device