You absolutely did the right thing.
He was probably quiet because he heard something in your one word answer that he is not used to.
Resolve.
Believe me, addicts are used to seeing wiggle room, and carving out a nice spot for themselves in your weakness.
No doesn't leave any grey area.
And in the end, if he feels alone, and helpless, you might be helping him to see how far he's fallen, and have to deal with the consequences of his own actions, which unfortunately is the best thing to starting toward recovery.
Propping him up will just prolong the sickness, the using, the excuses.
Good job!