Absolutely. I have very little doubt that it was indeed a nation-state who developed it; but, my main issue is with the distinction of it being a "wealthy" one. Couldn't Flame, perhaps, have been developed by Iran and released on themselves as a means for drumming up anti-Israeli or anti-American sentiment?
I realize something like that is totally conjecture; but, I don't see it as any further conjecture than, "it must be the US and / or Israel"
[Edit] Since somehow this didn't come across in my post; throwing up conjecture at another possible source of Flame outside of US / Israel doesn't mean I believe any of these explanations--my point was merely that both ideas are pure conjecture with little (at least that I'm aware of) evidence to support the claim.