I'm a righty, and my right arm is almost an inch bigger than my left. However, my left bicep seems to be stronger than my right sometimes while training biceps. Also the vein in my left bicep is more prominent than the one in my right... wut?
While the body is symmetrical it is not a carbon copy right to left. My vein patterns are different in my arms. Its not uncommon for the dominant side to be bigger. Calves, pecs you name you probably got one more developed than the other