I told him his poetry probably would not be published by a company
Why don't you think his poetry will be published?
He hasn't any experience writing poetry yet.
I understand, but you shouldn't go around crushing people's dreams. You should be more uplifting towards his work.
How? By letting him know that he can do whatever he wants? The kid can dream but he should get a damn life first.
I can appreciate that you don't want this person to pursue an unrealistic dream, but the manner in which you broke the news to him was highly inappropriate.  You should not have crushed someone's dreams in that manner, but rather, you should have encouraged him to write poetry as a hobby, while informing him of the reality that being published professionally is almost impossible.