As the others have said bad information from the petstore. When I was first looking at getting my angels I was told that a 5 gallon tank would be okay for 5 angels
Forturnately I did not take his word for it and did my research. I still started off with a tank that was still too small but quickly was able to find my 50 gallon. It pays to do your research and not take the word of most of the fish store employees. Some of them are knowledgable, but most are not and don't even have experience in keeping what it is that they are selling.