I have been keeping goldfish for years and the long finned varieties move exactly like that. I saw where someone thinks they bump the glass to much. They do that almost as much as they go to the bathroom.
The bodies are like the cheaper varieties you buy at the local pet shop. (a little long from head to tail). I realize that is probably the way most people see goldfish but it would be nice to see some with the show quality body type added at a future date.