Difference between 2.4Ghz ISM and IEEE 802.11 frequency bands?
I suggest that you first learn a bit more about wireless communications

Your question is like asking the difference between a concrete road and yellow cars. Both are needed to transport things and are not related but you cannot compare them directly.

A frequency band and a IEEE standard are related but different things. That ISM band tells which frequencies can be used.

IEEE 802.11 is a standard describing how the communications take place. It might dictate what frequency band is used but does not have to. Note how IEEE 802.11 is divided into many substandards like IEEE 802.11n which can be used at both 2.4 GHz or 5 GHz. IEEE 802.11a uses only 5 GHz.

Bluetooth also uses the same 2.4 GHz ISM band, that does not mean Bluetooth devices can communicate with WiFi devices (IEEE 802.11).

The nRF24L01 is just a transceiver, it does not "speak" WiFi (IEEE 802.11) so like Bluetooth, it cannot "talk" WiFi. Note how that chip has 126 RF channels in the 2.4 GHz band. Now compare that to what WiFi uses or Bluetooth.

The  fact that this chip does use the 2.4 GHz ISM band means nothing. Many devices and standards use this band because it can be used "freely" around the world. But in order for two devices to be able to communicate they need to speak the same language, in the communication world that is called a protocol. IEEE 802.11 is a protocol so is Bluetooth, HomeRF, ZigBee etc. They're all different protocols using the same frequency band.