RFE was about some specifics of why previous i-140 was withdrawn. It was technical.
My employer is a regular public company. I think what made my approval this fast was the fact that it was an exception case, which would not fall under normal processing process. My previous i-140 was withdrawn because wrong category (I am EB3 but original i-140 was filed under EB2 by accident). The re-filed i-140 case (under EB3) required IO to find the original i-140, pull original certified LC, and then attach to the new i-140. I think what happened is that when IO was doing the above, he just simply approved it right there. I think it was just luck. But it does not matter, as my category is not current and far to be current. So, I can't file 485 anyway.
I hope it helps. Let me know if you have questions.