Machaca
Frames are the "hoops" that run the circumference of the fuselage, and to which the longitudinal stringers are connected. The skin panels are then attached to them both.
Yes, it appears to me that object in question is a piece of frame, or a length of skin with a stringer attached that is bent 90º to appear on edge.
OK, I was using the word bulkhead for what you call a frame. But I'm still having trouble resolving from the incident picture what you show in the reference picture that you just posted. Could you circle or other wise identify on your reference picture what we think that we are looking at in the incident picture. My belief is this is critical to the chicken and the egg of what failed first