Not true, or rather, not completely true. It depends on whether you're talking from the point of view of the employer or the employee.
If I'm employing someone, a competitor can't easily employ them at the same time (sort-of excludable, up until they quit). And the costs of training an employee are usually fairly fixed - paying for a course plus wages - so they're rivalrous, since an extra training course will cost the same.
As an employee, on the other hand, I can certainly deny my training/experience to those who don't pay for it (ie. it's excludable).
The original point was that maintaining a pool of skilled employees is in the best interests of a group of companies even if they're rivals, since more people with the skill will tend to drive wages down. If, on the other hand, they neglect training and fewer people are available, then production suffers and wages go up. The "public" in this case is the group of companies.
If I'm employing someone, a competitor can't easily employ them at the same time (sort-of excludable, up until they quit). And the costs of training an employee are usually fairly fixed - paying for a course plus wages - so they're rivalrous, since an extra training course will cost the same.
As an employee, on the other hand, I can certainly deny my training/experience to those who don't pay for it (ie. it's excludable).
The original point was that maintaining a pool of skilled employees is in the best interests of a group of companies even if they're rivals, since more people with the skill will tend to drive wages down. If, on the other hand, they neglect training and fewer people are available, then production suffers and wages go up. The "public" in this case is the group of companies.