Another effect they're glossing over is inflation. They're measuring real labor productivity ((dollars generated / inflation) / hours worked), but usually the way you measure inflation in that equation is to plug in some society-wide metric like the CPI or GDP deflator. By most accounts restaurant inflation has gone up more than overall CPI inflation; at least, I'm spending $120 on a meal that would've cost $80 pre-pandemic, yet official CPI inflation over this time period has been only about 23%. If you use that formula naively, it looks like the earnings of the restaurant sector have increased (which, technically speaking, they have relative to the rest of the economy), but it's really because you're paying more for the same service than you did before.
No, they're not glossing over inflation, because they were able to explain nearly the entire difference in real sales per employee between restaurants during the same time as a function of dwell time.
They are not just looking at an overall increase in sales, misunderstanding sector-specific inflation, and saying it must be dwell time.
It's a good paper! I would encourage reading it. They have specific dwell time data per location, along with sales data, and explain the difference in productivity by looking at differences in productivity between restaurants over the same time period, find that it is determined by changes in dwell time, and then find that the overall mix shift of reduced dwell time explains the overall change in real sales per employee across the sector. Inflation is not the explanation.
