Yes they tracked hours of light exposure (above some threshold? I don't see that they say.) and found this result in the 90-100th percentile. So almost certainly night shift workers.
They grouped the population into percentiles with 0-50% having quite low exposure (0.62 lux median, range of 0-1.21) vs the 90%-100% percentile being 105 lux (range of 48.3-6400). You can compare the daylight light exposure to the nighttime and basically see what a shift worker would be.
But they already deconfounded for shift workers, so that's irrelevant. And they also showed the amount of light exposure for both night and day.
But they already deconfounded for shift workers, so that's irrelevant. And they also showed the amount of light exposure for both night and day.