My baby boy born 29 weeks 6 days stay in NICU 61 days

My water break by 29 weeks 5 days, while I went outside and coming back home. I was wandering why it's happen, even till now I am not finding reason why?? Everything was okay. After I came back home I identified that my water break at 2.20pm on 19 september, immediately I called my midwives they told me to visit them same time. When I went there they confirm it and immediately they called my hospital to admit me. But she inform me as it is too much early my hospital can not accommodate me they will send another hospital. It's happen my hospital admit me but after give a short in my hip they told they are transferring me. My labor pain start from evening. But another hospital they try to keep baby inside me. Doctor told me if possible they will continue Pregnency upto 32or 34 weeks. But in early morning labor pain come too much and suddenly Doctor  was found that my cervix was open and baby head coming out. Immediately they took my in labor room and my baby boy born at 8.03am September 20. Born weight 3 lb 5 oz. he was healthy no complications except premie. He was in NICU 9 days then he was in continue care nursery upto his 2 months birth day. He was discharge November 20.... Discharge weight was 7 lb 0.9 oz... Al Doctor and nurse in NICU was very good. They teach me lots... Day by day I learn more in our 61 days journey... He is in home now doing very well... Increasing weight... But still his born is misterious why he came early!!!