What he is saying is, while a lot of the phone calls you got were answered with the KB, this doesn’t reflect the people who didn’t call because they used the KB. For that, you would need to track total sales, new customer intake, volume over time, etc. It’s quite possible you could have customers who got a KB reply from your support staff in a timely manner and decided if it was that easy for you to get an answer to them, it would be worth it for them to try it before calling next time.

Of course, the reality is quite likely that the main users of the knowledge base you built was the support team, which still isn’t a loss.