Well,
If you wanted your kid to stay small, would putting him in a trunk work ?
You can't make any animal stay small by keeping it in a small habitat. The best case scenario is the animal gets too big and forces the owner to get a larger habitat or re-home the animal. Worst case, the animal ends up sick or stunted and dies much too soon.
This persistent myth does a great deal of harm in both the fish and bird world, and it's a pity too many people out there believe this garbage. Not only that, media perpetuates it. How many TV shows and commercials have you seen that show a large 4-6 inch goldfish in a 1 gallon fishbowl? And how many fools out there kill these beautiful creatures because they believe you can do that?
I'm glad the OP has sense enough to question what he/she read, but a lot of people don't.
Gale