My understanding is that "Medicare for All" was deliberately a fairly ambiguous phrase until recently, which was inclusive of a range of proposals including what you might now call a public option or Medicare-for-All-Who-Want-It.
So if Buttigieg had said "I support eliminating private insurance" or "I don't think a public option is going far enough" or "I support Bernie's plan", then yeah, he's flip-flopped. But there's a lot of revisionist history here about what M4A meant, especially circa 2018.
I have receipts, too. vox.com/policy-and-pol… 
It's not just that M4A was an ambiguous term circa 2018, but that it was *deliberately meant to be ambiguous* to advance progressives' argument on health care. So it seems like super bad karma if you're a progressive criticizing Buttigieg now for working within that ambiguity.
