You entered the US on 7/1, your AOS package was delivered to the Chicago Lockbox on 8/11. I would be pretty much skeptical about your claim of not having a preconceived intent of filing AOS before you entered the US if I was the IO. As the IO, I will find it rather unusual for a genuine visitor to travel to the US with their birth certificate and educational documents - documents you would have included with your AOS package right? You were also able to make the DV administrative fee payment within that short period of time. In addition, this visitor has been able to secure a job offer between when their AOS package was filed (on 8/11 and 9/23 interview date) and present that offer of employment letter in support of an AOS application that was not pre-planned prior to coming to the US.
So yep, seems like the IO had second thoughts about your case after initially approving it, hence the request for you to return to the FO. It is possible the IO believed your explanation. Anyway, you’ll just have to wait and see if the approval stays, in that case the GC will show up soon.