The pet store I go to knew cedar was bad over 10 years ago, when I bought my first corn snake.

As for the growth, 2 inches does seem a bit much for 11 days. However, it's not uncommon for a ball python to grow 2 feet its first year. I'm not sure where your figure of 1 foot comes from, but my guess would be that 1 foot would be the average after taking into account all the ball pythons on maintenance feed. Thus, 1 foot for a ball python fed weekly or more would be fairly conservative.