The article is correct that recreational books are below for cumulative CPI. College textbooks on the other hand are at ~ 3 times the rate of general inflation.
Source:
BLS CPI-U (FRED: CPIAUCSL)
BLS "Educational Books and Supplies" (FRED: CUSR0000SEEA, ~767 in Mar 2026, base 1982-84=100)
BLS "Recreational Books" (FRED: CUUR0000SERG02, base Dec 1997=100, recently ~96-100
(just search for the above, and follow the link to https://fred.stlouisfed.org)