N-400 RFE asked at the day of the Interview

My friend had a naturalization interview on June 28. He passed the tests, but they asked for tax transcripts for the past 3 years and proof that he is current with all of his income state tax obligations. 
On July 11 he went in person in Chicago USCIS office and gave the required evidence. On the same they, he received email that a recent action was taken on his case. The online status was saying that request for evidence was asked and he has deadline until June 28 to do so. Once again, he gave them the required documents on July 11.
Yesterday, August 10, he received email and online update on his status which says:
Response To USCIS' Request For Evidence Was Received
On August 10, 2016, we received your response to our Request for Evidence for your Form N-400, Application for Naturalization , Receipt Number NBC*********Our Chicago Field Office office will begin working on your case again. We will mail you a decision or notify you if we need something from you. 
Why does it says that they received the response on August 10, when he personally gave it to them on July 11???? How is it possible for them to never got it for a whole month?
What is going to happen next? How long does it usually takes for them to make a decision after the response was received? Any experiences?