The 23-year-old's second-half strike was enough to hand the Red Devils first place in Group G and a last-16 match against Japan.
Speaking to The Mirror, former Manchester United player Januzaj addressed the "criticism" that he faced in England and said that he wanted to "show the people" his ability.
"Obviously my job was to show the people, in the past in England, I had a lot of criticism," the midfielder said. "I wanted to show those people that I'm here. I'm very happy with that. I'm very pleased to score a great goal against a good opponent.
"I've put in a lot of work. This year I've been playing in a team at Real Sociedad who have made me grow as a player. At 23, the most important thing is to play games and keep progressing. I'm very pleased to be going that way.
"I hope now to keep going. My first goal, there is no greater feeling. I was very pleased with that, and hopefully there'll be more to come in the future."
Belgium will face Japan on Monday evening.