Mine is exactly same as yours, my interview was on the same day as well. The interviewer took all the job documents and retained passport as well. I got a call from the consulate on 14th March, I was asked few questions about the client and to submit vendor letter to the same email id that you mentioned. All are clear/ perfect on my side.
I have been working for the same client for the past 4 years, which is a very big US company.
When did the client get the call after you submitted the document?
I did not receive any email from them saying they received my document, did you get the email on the same day ?