Hotspots in the cylinder would not turn the motor over inadvertantly. Seems to me that you may have a faulty starter solenoid. The solenoid is an electrically operated switch. The switch contacts are held apart by a spring. When you turn the key to start the car, you introduce a voltage into the solenoid to activate an electro magnet. This electro magnet moves a set of contacts, over-riding the force of the spring, to allow a large current to pass through to the starter motor through these contacts. If the spring is weak or indeed broken, you could get uncommanded starter motor operation. You will need to get the starter either overhauled or replaced.
