Rain probably tried to force Recognition, but he might not have been totally successful. Pike says, in Hidden Years #5: "Careful, sire Rain! I was your first try, and look what you got!" Also, there's a caption that goes: "Rain's smile fades. He cannot truly force Recognition."
So what might have happened is that Rain tried to force Recognition, but failed. However, by a lucky fluke, Pike's mother got impregnated.