Got an RFE because Officer made a change (mistake) in the application during I485 interview

[BBME_043]

My wife (LPR) and I had a I485 interview last week at chicago field office. The interview went well and IO said she would approve the case and I should receive the green card within 4 to 6 weeks. Today, I received a letter from the field office asking me to submit the proof of my wife's US citizenship and an original copy of her birth certificate within next 2 months, otherwise the I485 application will be denied. I was really surprized, then I realized the officer made a change in the application during the interview. At that time I did not realized it was a mistake because she did not read out properly.
This was how it went "Officer: You chose another relative in your application but as a spouse you are an immediate relative. I am correcting this. Me: Sorry about the the mistake".  
After looking at the I485 application form, now I realized what mistake she made. It is in Part 2 question 1a (I am applying to registered for LPR or adjust status based on the following immigrant catagory : option-1) immediate relative of US citizen; option-2) another relative of US citizen or relative of a LPR. In my application I choose option 2 which she changed to option 1. I did not realized it at that time, trusting what she said is correct. I don't know why she did that. She even looked at my wife's passport (not a US passport) and green card.
Although this seems very rare case, did anyone experience similar situation of officer making a mistake during interview? I would really appreciate any suggestions regarding what step I should take to correct this or how I should response to the letter I received from Chicago field office. Or, I must consult a lawyer before talking to USCIS.

[pontevecchio]

Get a lawyer involved if you want to avoid months of delay.