You may want to consider a bigger tank for an adult peacock as it will provide a lot more entertainment if they have plenty of area to explore.
That being said, I would keep the one you have as she/he seems very entertaining!!
I am guessing whoever said that was misinformed because they are identical coloring, just smaller.
Here is the one I had many years ago... she ended up constructing a tunnel the entire length of the 20g long from one end to the other.
Yeah, I actually have a 40b lagoon tank planned for soft corals and the mantis, long term. I have the stand, just need to get the tank during the next petco $1 per gallon sale. I am out swapping the little guy for the 5” peacock right now. Impetus to get the larger tank sooner rather than later.