The Sweden winger left Manchester United for Forest 18 months ago.
He told The Athletic: "I made the right decision, 100 percent. I haven't really talked about it here, but at the time at United I was very young and I came into a team that was struggling.
"Yes, I had the idea that 'I play for Manchester United'. But I also never felt like I was getting better. I played for the cause when I got the opportunity from the bench.
"Coming to Forest was so big for me, because suddenly I was regularly playing 90 minutes, while having the opportunity to develop. When I played, I felt like I had a purpose: like I was playing and improving in the process.
"That was the biggest change for me. I feel like I know the league inside out now, because I've had the chance to learn. I have no regrets, because I enjoy playing great football with this team. We are in a really good place at the moment."