Not to sound like an egghead (though given the above sentence, I guess it's too late), but poppycock.
The zone of proximal development is supposed to be exactly where learning happens, insofar that it is a smidge above your current knowledge comfort zone and thus requires a bit of cognitive stretching. The flow state is not a learning state but the interface of optimal productivivity and creativity. Time collapses and distraction fade to oblivion. Not the same thing at all.
As for reflection being required for learning, Quinn doesn't cite any research at all, though a quick google search brings up the following on Brock University's website: "Reflection is not a superficial process of introspection. Rather, it is an evidence-based, integrative, analytical, capacity-building process that serves to generate, deepen, critique, and document learning. Additionally, the development of reflective skills is central to students’ academic and professional development within a discipline. The ability to reflect on one’s practice when confronted by a novel, unusual, or complex situation distinguishes expert practitioners from novices (Schön, 1983)."
Cognitively, there are two perspectives here: one has a lot in common with rehearsal, while the other is more amorphous but related. Many studies have shown that "sleeping on" a problem is a shortcut to solving it, and that kind of unstructured unfocused cogitation is a significant element in the learning journey.
The ability to reflect also shows up in the wisdom literature as one of the distinguishing features of a wise person.
But... just because it's a facet of learning doesn't make it necessary. Vgotsky's theory relies on the same kind of unconscious reaching involved in the "sleeping on it" example above, but in this case the brain is stimulated to produce new neural connections by making new intellectual connections, trying to stitch new unfamiliar knowledge into the existing cranial quilt. That's a different task than reflection, but there's no support, in my opinion, for the argument that therefore learning is precluded.
I don't know exactly to what lengths I'm willing to take this argument (as if anybody's reading anyway), but I do hereby invite Mr. Quinn to get drunk someday post-covid and we can duke it out if need be.
aka The Cogsci Pugilist