Whose assumption is wrong? Every answer you have gotten is spot on correct.
I don't have to say any more about the strict requirements of heat, humidity, digital thermostat, and probed digital thermometer for ball pythons. These things are absolutely required for this species.
BPs are notorious for not eating and quickly getting respiratory infections (which can kill and are expensive to treat) if the husbandry stats are not met.
Such a young baby will not fare well without the proper set up. If you purchased it from a chain pet store, even if they told you it ate, chances are it has not. If that baby was a wholesale captive hatched baby from Africa, like most baby BPs at chain stores are, it was shipped to the pet store before it ate. The stresses of the trip and inadequate husbandry at these stores would mean the baby would not have eaten for them if they tried.
No one is bashing you. They are trying to help. Otherwise you will most certainly have a sick and eventually dead baby on your hands.
Follow the care sheet. It's not very expensive to get these things.