How is it possible that my passport before the renewal was ECR and?
There are different criteria to qualify for ECNR such as age, qualification etc. Also criteria has been relax a bit in last few years. So it is quite possible that earlier you were not qualified for ECNR but now after 10 years when you applied for renewal, you are eligible for ECNR. Another reason could be that while you applied for first passport, you didnt mention that you are eligible for ECNR, so even you were eligible but you didnt get ECNR but this time when you applied for renewal either you selected ECNR or system auto-detect that you are eligible for ECNR.