All capacitors have series resistance and inductance. The resistance is from the material in between the plates of the capacitor (and a small amount from the leads and metal). The metal in the plates and the leads contribute a small amount of inductance. The combination of the resistance, capacitance and inductance make an RLC filter.
The resonance point mainly depends on the capacitance but can vary with package size. Because of this if you want to lower the impedance of the capacitor, its better to parallel them, one with a lower resonance point and one with higher (which correspond to lower and higher values of capacitance). So the designer of this circuit was trying to lower overall impedance (probably for a faster rise time)
You can see how paralleling two different sizes of capacitors (red and blue lines) lower the overall impedance (cyan line). Just check the datasheets for the ESR and ESL values or some will also include an impedance graph such as the one below.