Well, how did your sponsor pay your expenses? Was money transferred into your bank account, did they pay college/rent etc directly, what? I have to say I have not personally heard of this kind of RFE for OPT before, and reading between the lines by looking at what they are asking for, it sounds like they are concerned that you may not have maintained status. So to go back to what mom said, it may be in your best interest not to just leave this hanging, even if you only need to respond by October.