Not for there whole life span of 20+ years!
The reason they need big tanks is because goldfish get big! Most get at least 12 inches, some can get a bit bigger! By keeping them in a 5 gallon tank, you have severely stunted their growth.
So, no, it does not prove a thing. It proves that YOU...
You are not underfeeding. Over feeding would be anything over 3 to 4 pellets two times a day.
What is her home situation? What sized tank? Does it have a heater? A filter?
A proper betta home will be between 2.5 and 5 gallons at least. Since betta are tropical (warm water fish), it would HAVE...
If the small tank is 5 gallons or less, then it is WAY overstocked! A 5 gallon should only hold a single male betta!
If you get a 10 gallon tank, you need to move all the neon's to it, as well as the corycat. THEN, because cory cats are schooling fish that like to be in groups of 4, I would add...