0 volatility does not mean 0 movement, it means the lowest probability for movement. Just like a 100-skilled catch WR will not catch 100% of the passes thrown to him. Nothing is absolute.
However, that -3 could easily be recovered during the season, because 0 means he has just as much chance of going up as going down and the amounts will be very small. Remember, too, that a player's first training camp and first season will have a significant amount of movement as opposed to the rest of his career.