I do not think 2.4 GHz is the processor frequency - most high-end smartphones with significant gaming orientation only run on up to 1 GHz these days, and it is not like clock speed means ANYTHING AT ALL without details about the type of processor.
The 2.4 GHz likely refer to the wireless connectivity, as the range around 2.4 GHz carrier frequency is a range without monopolistic licensing, which allows its use for various connectivity technologies, such as WiFi, Bluetooth, Microwave ovens and quite a few proprietary RF links. Not linked to clock speed at all, and conforming to a standard already present in the original DS, which had 802.11b WiFi at 2.4 GHz.