I can understand why you asked this question, as you do sometimes hear people talking about "small angels" as if there was such a species. It's ignorance, most of the time; some lfs staff only see the fish when they are juveniles sold by the shop, so they don't realise how big they grow. I've even seen a RSPCA publication referring to fitting "small angels" into a small tank- as if they would never grow up! A bit like encouraging people to buy "mini-St Bernard's", meaning puppies. Good job you're doing your research, it is easy to get sold a pup!