Googling around, I find:
“C’est donc une revolte ?”
and the response: “Non, Sire, c’est une revolution!”
Is this the accurate French version?
Yes it is. Although I think a king would do the inversion and say “Est-ce donc une révolte ?”, which is a higher register turn of phrase, and the way my grandma always told the story.
But since no audio or video evidence has ever been produced, who knows what his exact words were ? “C’est donc une révolte ?” is perfectly valid French.
Not necessarily. “C’est donc une révolte?” and “Est-ce donc une révolte?” have a somewhat different meaning : “So, it’s a revolt?” and “Is it a revolt, then?” respectively.
Patiently waits for the straight line
The peasants are revolting! okay