Thrust is the reaction force derived from a rocket nozzle. You don't have to have combustion or fire to create thrust as evidenced by simple soda bottle rockets that use water and compressed gas. But in spaceflight combustion is one of the more efficient ways to create thrust in terms of the energy produced and weight of material required to derive that energy.
The force of thrust is derived by momentum exchange. The rocket throws off many small particles of mass at high velocity in one direction and by Newton's third and second laws, the spacecraft is accelerated in the opposite direction.
For fuels that do combust, a thrust chamber is engineered which allows the combustion to build a high pressure, and at one end of the chamber a nozzle is fitted that retains the chamber pressure and increases the velocity of the thrust. The magnitude of the thrust force is roughly the chamber pressure times the nozzle cross sectional area.
For the butane lighter there is no thrust chamber, and the combustion takes place in the atmosphere where pressure can't really build up. If there is any thrust to consider it only comes from the expansion of the butane gas from the valve opening, before combustion takes place. And I'll wager its on the order of micro-Newtons.