Determining Enthalpy Change of the Combustion of Ethanol

A worked example went something like this:

Use the following experimental data to determine the enthalpy change when 1 mole of ethanol (C2H5OH) is burnt:

Mass of water = 150.00 g

Initial temperature of water = 19.5 °C

Maximum temperature of water = 45.7 °C

Initial mass of spirit burner = 121.67 g

Final mass of spirit burner = 120.62 g

Being a worked example, I saw the worked solution and understood the process completely. What's bothering me is a fundamental flaw in the procedure that has seemed to be neglected completely.

We are relying on the idea that the combustion of ethanol will produce some energy, the amount of which can be calculated with the increase in temperature of the beaker of water on top. However, if there was no ethanol, no combustion, the flame giving rise to the combustion would still manage to heat the water up; in this sense, we do not know whether it is the flame supplying the energy to the rise in water, or the exothermic reaction that takes place with ethanol. How does the existence of such a flaw make the procedure useful to any extent? Is there anything I'm missing?