Well your partly right and partly wrong with Boyle's Law.
Remember, the can of compressed "gas" that you have and use to blow dust off your equipment is actually a chemical gas. It used to be dichlorodifloromethane which was a florocarbon, however I am not sure what the newer non FL
This gas is held in a liquid state (shake the can, the liquid sloshes) because the vapor pressure of the gas above the liquid in the can is sufficient to stop the liquid from boiling. Note that this gas boils at a very low temperature, unlike water which boils at 100C.
When you spray the can, you release the pressure above the liquified gas and it starts to boil. If you remember your physics, it takes a tremendous amount of heat to change the liquid to a gaseous state.
This heat comes from the walls of the can which is why they cool down very quickly. If you are holding the can, this heat (energy required to change the state of the liquid to a gas) also is taken from your hand.
Therefore it is not only the loss of pressure as per Boyle that reduces the temperature, but it is also the change of state that requires heat energy.