I'm assuming that average that you're posting is just the average of all the salaries listed in the data provide. This includes all the administrators (as far as I can tell). To be a useful comparison, you'd have to include all the salaries of the administrators OR only average the union workers with 10 years of experience (or whatever is the equivalent of a teacher with 10 years of experience).

Interestingly, where did this person get this data? Is it publicly available?