Being 65 doesn't necessarily mean one should or has to stop workin'.
If the term "participation rate" were to be expanded to include the number of workers divided by the TOTAL NUMBER OF "peeps," then a sudden, large number of babies being born in a particular year (something having no bearing on the availability of jobs, or of labor) would have an enormous impact upon this "rate" - thus making the "rate" useless for economists / labor experts, etc.
The real answer is that the writer of the article used sloppy language and/or logic.
Regards,
True, but for statistical purposes the working age population uses age 65 as the end of working years. Doesn’t mean many people don’t continue working past that age.