Lower back rounding and lower back strength

[kabuki]

I read somewhere that if one's lower back rounds even at a light weight, it is a flexibility problem, but if it only rounds at a heavy weight, then it's more of a lower back strength problem. How true is this statement?

EDIT: This is about low bar squats. I can't believe I didn't even mention the name of the exercise when I first wrote it, haha (although you could have figured out).

[MikeC1]

That sounds about right, though I would say that if it happens at a low weight, it could be a body awareness problem and not necessarily a flexibility problem.