Higher octane fuel doesn't burn any hotter than lower octane. If that were the case it would cause detonation. Higher octane fuel has more resistance to break down into elements that can start the combustion process from the heat in the cylinder, and not a controlled spark.
Higher octane fuel has the same flame front speed as lower octane, there are slight differences, however they are too small to even be a factor.
Gasoline when vaporized/heated starts to degrade into seperate flammable elements, including free Hydrogen, and elements containing Hydrogen. These can burn with much less heat to start them off. What happens in the cylinder is as this uncontrolled flame front burns, it creates more heat in the cylinder, causing the remaing fuel to degrade and auto ignite, the gasses create more pressure as they expand,and are compressed by the piston. More pressure, makes more heat, and the visous cycle continues. Detonation.
High octane fuels have stronger(chemical) Hydrogen bonds, and don't give up free Hydrogen as easily. And they resist breaking down. Heat can come from compression, left over spent gasses, even a burr or piece of carbon on the head or on a piston.
A Ignition spark that comes too early in the cycle, causes the fuel to start it's burn, heat is released as the piston is still compressing the air/fuel mixture, it rapidly degrades from heat of the burn and compression(from the piston, and expanding gasses) , then auto ignites(explodes) and you hear a "knock". This is pre-ignition.