The technique is similar to that used with other single pixel cameras. The trick is to first randomize the light that the pixel detects, record the resulting light intensity, and then repeat this process thousands of times.
It’s easy to think that this randomization makes the task of creating an image even harder, but the reverse is true.
The randomization process changes the intensity of light each time the pixel records it. These differences in intensity are not random but instead correlated with the scene in front of the pixel. So producing an image is simply a question of mining this data to find the correlation. And the more data that is collected, the better the image becomes.
So by recording the intensity of light many times, it is possible to create a high-resolution picture with a single pixel.