Factual error: During one scene where Ronald is giving lessons, he tells Cecile to play a G major scale. After he says this, he adds, "Remember the third note, it's sharp." In a G major scale the third isn't sharp. The seventh is. (00:18:35)
Suggested correction: When playing the cello, there can either be one finger space between the two notes or two. The first G would be just the G string with no fingers. The second note would be A, which means just putting a finger in the correct space on the string. The third note is B. The third note would use the third finger. The alternative, which would be wrong, would be to use the second finger. What Ronald is saying is, rather than use the second finger, you should use the third finger.
This correction seems to validate the mistake. There's nothing in the quote to indicate he's talking about finger positioning, you're not playing a sharp on the 3rd note.