I don't stutter too when I'm alone. Neither when I'm singing, using fluency techniques, slowing down, reading etc. But I still stutter. Stutterring is a neurological condition enhanced by anxiety. If you feel less anxious while speaking, or if you use different neuronal network by singing or using a metronome for example, you're going to stutter less or don't even stutter, but there's still differences in some part of your brain. That don't mean you can't work on your stutter (the examples I cited could be helpul if you want to be more fluent), but that's almost impossible to absolutly get rid of this.