In the smaller package the pins are closer to each other, but the lenght and area is also smaller. With a coax cable the capacitance per unit length only depends on the dielectric and the ratio of inner to outer diameter, not that absolute scale. So though much smaller distance a thin cable of same ratio would have the same capacitance per lenght. A similar scaling should apply to a scaled down leed-frame: similar capacitance per unit length and thus less capacitance for the smaller version.
Similar parasitic inductance can be smaller for the smaller case version.
It is already odd to find such a fast amplifier in the large DIP case.