You have high chances of your US visa getting approved if the interview officer really said this. But even that doesn’t guarantee you getting the US visa. There are a lot of background checks that they run and while a lot of things lie in the officer’s hands, there are some things out of his control too. He can solely reject your visa but cannot solely grant you one.

When we went for our US Tourist visa interview in September 2010, we were told the same thing. The officer said that he would be approving our visa and even though that was a good thing to hear, that’s not the final decision. The officer will be sending their positive or negative feedback to the Consulate, which in turn, will decide whether to grant you the visa or not. But if all the documents are correct and the interviewing officer is satisfied, unless there is some problem with your application or supporting documents that the officer overlooked, you will be getting the visa.

Also, keeping the passport with them is the standard procedure. Even if they were to reject your visa, they would keep the visa with them only. If your visa is approved, you will be getting the passport over courier with the visa, in the form a sticker. If rejected, you might be getting a ‘Visa Cancelled’ stamp on your passport or a letter mentioning that your visa application has been turned down. The passport will be mailed to you in both cases.