That's basically what he said. You're doing something that you'd ordinarily find boring, but now you don't feel bored.
Feeling bored is your mind telling you that you should be doing something else.
Okay - so you normally would feel unpleasant. Now you don't because of weed. Of course you can argue weed is unhealthy - totally possible. But regarding the perceived state change. How is that causing harm? Because s/he's not going to become wealthy or "successful"?
The problem is if you do it to excess. When you would rather stay in and get high, than meet up with friends, drop out of school etc. When you are not living up to what you consider successful for yourself. Then you have a problem.