I actually wouldn't be surprised to find that most labor markets are bi-modal (but certainly not all). Which is why I used median wage and not average wage, because the median is very likely to grab the common tradespersons compensation experience whereas the average is likely to be skewed high by the upper distribution group.
She describes it as a bimodal distribution. One (smaller) group of people with trades are willing to work anywhere whenever. They work in fly-in camps with limited work seasons and practically unlimited overtime. Since there’s nothing else to do, they log enough hours to get into double and triple time. The other (larger) group goes home after work and their overtime is limited to nonexistent. The pay is so different between the two groups that if they’re analyzed together, the statistically typical tradesperson looks nothing like the typical tradesperson.