It actually doesn't say that in our letter. It just says if you want to submit a reply please do so within 10 business days of the date of this letter. I suppose this is the reason why I started updating this post because it's all so darned unclear.
The short answer is yes if you don't reply it goes automatically to appeals. They take a preliminary look at your file and then give BDO a list of items required to make a determination. They then communicate it to you and you have 20 working days to respond.