No he wasn't, he's probably been irreparably damaged already by your cruel insensitive practices. In England you could be arrested and charged with animal cruelty for keeping a fish in conditions like that.
Not just too small .... WAY TOO SMALL, A suitable tank would be over 10 TIMES LARGER ... That's 1000% bigger get it ?????
It either comes naturally to you (as I suspect) or your not trying hard enough.
So your not really looking for genuine help (ie: the truth) you just want to hear that your doing the right thing regardless ?
no filtration system will help given that bioload ...you would have to do 2 50% water changes a DAY to even come close ...
You refuse to accept the facts, this is not anyone's fault but your own.
No, this is not normal behavior but your fishes symptoms are common in severely stunted stressed fish in poor water conditions.
If you really want help then post your full water parameters
PH, KH, Temp ,Ammonia, Nitrite and Nitrate readings (yes ALL of them ...if you don't have the test kits BUY them), your full stock list, water change regime, filtration systems, feeding regime
AFAIAK is you cannot provide the above experienced keepers here would be unable to help you or your unfortunate fish.