Disclaimer: I am not an electronics engineer.
If you look at the block diagram (section 7.2/page 10 in the LM36922 datasheet), these frequencies appear to be for the boost converter which is used to generate a voltage higher than the input voltage in order to drive long series strings of LEDs.
The boost converter comprises some control circuitry, a FET shown in the block diagram and a 10µH to 22µH inductor shown in the simplified schematic on the first page of the datasheet. Like other kinds of switching power supply, as found inside phone chargers and PC power supplies, this will generate pulsed DC at the required voltage, which can then be smoothed into ‘normal’ DC. There is a 1µF capacitor shown on the simplified schematic, which may well smooth the pulsed DC to create non-pulsed DC. There will always be some ripple from this kind of power supply. In applications where low-ripple is important, voltage regulators can be used to chop the ripply bit off of the top of the waveform, after smoothing with a capacitor. The LM36922 probably doesn’t support adding a voltage regulator, but it’s less important for LEDs than it is for microprocessors and the like. If the waveform is smooth enough, then the LEDs won’t be leaping from fully on to fully off and back again. Instead, they’ll just be dimming by some amount at the frequency of the ripple.
The other end of each of the LED strings is connected to a current sink circuit, which is what actually controls the brightness. There isn’t much detail about how this part works, but in the absence of any information about its switching waveform or anything of that nature, I would assume that there is no switching and it just sinks the specified DC current with no measurable funny business.
The LM36922 does accept a PWM input, which can be used to specify the current with which to drive the LEDs. Alternatively the current can be specified using an I²C serial interface. Both methods result in the current being set in the same manner, they’re just different ways to input data into the chip.
So, I can’t see anything in the LM36922 datasheet that suggests that the LEDs are driven with PWM.
(Edit: After re-reading my own post, I decided I should be a bit more circumspect about the smoothness of the DC supply for the LEDs, so I’ve edited my wording. I still believe it’s likely to be pretty smooth, but i want to be careful not to make claims I’m not expert enough to support, and I don’t want to imply that the supply to the LEDs will be as smooth as the DC you might get from a PC power supply.)