he's referring to labor productivity, e.g., the economic value produced per unit of labor input. it also _has_ changed significantly, as seen here: https://fred.stlouisfed.org/series/OPHNFB

however, unit labor costs has also been increasing (although they remain variable): https://www.bls.gov/opub/ted/2026/productivity-up-0-3-percen...

Probably to referring to hours worked, eg. https://fred.stlouisfed.org/series/AWHAETP