I view this as an angelic civilization before Adam. Of course, this is just a "theory," as with the Gap. I wouldn't state it dogmatically, nor would it stop me from having fellowship with other believers that do not hold to it or to the GT. There are things in Scripture that we may not fully understand, and some things God did not state unequivocally. Scripture must be compared to Scripture, and, sometimes, it is logical progression and deduction that allows us to arrive at a conclusion. And, sometimes, we just have to rest in the fact that we may never know something unequivocally, but, God does.