yeah he is right. As discussed most of the times, itÅ› not completely depends only on traffic. But you ad implementation and smart use of referrals depending on site category is important
look at your "Page eCPM". If it's $2.00 per 1000 impressions, you will need 15,000 impressions to make $30 per day.
But realize also that eCPM often times goes down somewhat the higher the impressions go. It's not always a linear plot.
You can get a rough idea. Of course, since it's all based upon past performance, "rough" is about all you ever get. It makes a difference how close he is to the 28-30 dollar range, too, as far as how accurate the extrapolation will be. If he's making 20 now, that's one thing, but if he's making only 2 a day, the error bars are pretty wide.