They could have been runts. I always have some angels that for some reason don't seem to grow like their brothers. They will be dime sized and their siblings are quarters approaching half dollars. I don't know if they ever catch up w/them because I don't keep them to see. If they were in a store display tank I would guess that they were underfed and did not develop correctly. If you ever want some runts to see how they grow let me know and I will tell you what I have available.
HTH,
HTH,