The egg was fertilized in one of Fallopian tubes (there are two) and the fertilized Oocyte failed to travel into the uterus where it would attach to the uterus wall. Instead it attached to the Fallopian tube wall. The baby grew and the tube burst allowing it to grow in the abdominal cavity (not the stomach). I wouldn't expect trans men, trying to implant a fertilized Oocyte in the abdominal cavity, would set up a fatal catastrophic event not as fortunate as what happened to that lady.
