No, they could not.
What does that even mean?
True. Science doesn’t do proof. That the hairlike fibers are homologous to feathers is an inference from phylogeny. It also matches a priori models of feather evolution, predicted (!) before the discovery of feathered dinosaurs. Incidentally, there are plenty of feathered dinosaurs with clear and complete feathers.
Does that mean that insects are not alive but earthworms are?