Hi Pitchounette. I think you handled the situation in true Kohn fashion. I can understand you feeling sad that your ds said he felt afraid of you; I'm easily hurt by the things ds (3) comes out with sometimes ("I hate you," etc). Is it possible that he knew he'd done something he shouldn't have, and was afraid of how you might react, rather than of how you did react? If you raised your voice/shouted a bit, when you disciplined before, maybe he was remembering this and feeling afraid of a similar reaction. Alternatively, because you sound new to Kohn's style, could your ds have felt a bit unnerved by you reacting to him in an unusually, even strangely calm way?
Agree with cockles, in that discipline (in the pure sense of 'teaching', rather than how it's commonly thought of - punishing, etc) is a cumulative process, and Alfie Kohn's approach is probably slower still; it's a softly, softly method. I sometimes find that hard, because I think: is ds still going to be doing [some typical, challenging thing that three-year-olds do] when he's 20?!
We find Kohn-style parenting hard enough with one - because it's so unfamiliar to us, I suppose - so I say well done for really going for it with two.