After a few days of research, I found out the answer. The question had already 3 votes and I answered the question. Shouldn't this generate a "Self-Learner" badge?
The answer must receive a score of 3, not the question.
Your answer currently has a score of 1, so you'll have to wait and see if it'll receive enough upvotes. If it hits a score of 3, you'll be eligible for the self-learner badge.