I do not have inside information but it seems obvious to me that files are subject to approval from more senior officers or managers. It might be rare that they overturn what the interviewing officer recommends (either way) but not impossible.I agree with Armoured
The interviews are recorded on the camera, even if they announce "Refusal" in the interview, they do watch the interview again & again before issuing any Refusal because they do not want to loose the case in case the applicants opt to appeal, they can loose their credibility if the appeals are successful repeatedly. And I am sure there are their managers/supervisors too to review these interviews before refusing.
In my case the Visa Officer said to my wife that she will send an "Refusal Letter" in two weeks, it has been three weeks now, we instead of getting a Refusal got Pre-Arrival letter, even for a moment if we think that it was a mistake then why they started doing Back ground check and showing "In Process" on the on GcKey it is showing that the Interview was completed on "June 21st" though the interview was held on June 02nd. Also No decision has been made yet its showing "Your Application is In Progress"
Maybe there was more going on, like officer saying rejection to see the reaction, but no idea about that.