I think you were probably very lucky in that case. The avoiding zone 1 fare is £6.25 and a similar zone 3 fare using Underground as well is £6.10. When you write again, maybe just comment on what the fare finder says and don’t mention your recent experience. Just say that travelling via Leyton and Harringay avoids both zone 1 and 2 and should therefore be cheaper than the other alternative fares.