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This has to do with the difference between isothermal and adiabatic processes. In the first situation, heat can be exchanged between the system and the surroundings. As a result, unlike Adiabatic processes, even though you are doing work by blowing air, the free exchange means that the temperature does not necessarily change. This means the process will be iosthermal (meaning the temperature will be constant). However, in the second case, the system rapidly loses air through the small hole, making it an adiabatic process (no energy is lost to the surroundings). Because of this, the fact that the air (the system) is doing external work means that it must cool down for energy to be conserved.
