I think it would go both ways, like a full audio interface.
In any case, you would have the option of direct monitoring your guitar before it goes into the computer. But I assume you are asking about audio coming out of the computer, like the other tracks playing in your DAW.
In the video, we saw four channels going from the Kemper into the computer. That would be an improvement in itself, as S/PDIF only provides two input channels so you can't combine a stereo signal with an additional DI signal. With four channels of USB audio, you wouldn't have to choose anymore.
But Christoph Kemper also said in the video he uses the Kemper for recreational listening now, taking advantage of its excellent analog outputs. That would suggest the USB connection is able to receive and convert digital audio from a computer. So, both ways!
All speculation of course, going from the video! 😀
I would expect the same - this two way traffic on the USB interface is necessary for ReAmping via USB of course.