If you don't see Developer Options anywhere in your System Settings, then it wasn't turned on, and this wouldn't be the cause of your issue.
The Developer Options menu by default is not activated--you have to go to Settings>About Phone and tap Build Number 7 times. This activates Developer Options and allows you to tweak various settings, one of which is the ability to keep the screen on all the time while it's plugged in. Sometimes the cellphone store rep might turn this on while they're transferring your data from another phone to the new phone, just so that the screen doesn't keep turning off while they're working on it. Then they forget to turn that feature off.