Not even that - the article only claims "25,000 messages". Multiple messages in the same conversation, as well as multiple conversations with the same person. The number of _people_ may have only been in the high hundreds…
The percentage isn't that great, but we usually aren't the ones initiating conversation. The quality is definitely what drives us to continue using it.
Olark has a free trial. When we first put it on our site we were pretty hesitant too, but after the trial we were sold.