Maybe I am being absurdly pollyanna, but isn't 'you would have known if you'd come to our open day' just, you know, a comment? If you'd replied 'oh, we did come', isn't it possible they'd have said 'oops, ok then, the answer is ....'?
I may be wrong, but my impression - based on two universities at a very low level, so I am sure it's not saying much - is that it's just vanishingly unlikely the same people are involved at all the different levels people mention, with this level of cross-checking.
I'd have thought that there will be several groups:
- the people who do open days, many of whom will be students/ postgrad volunteers as well as employees, and academics doing this because they want to meet prospective students they might get to teach.
- the people who keep records of open days, who will meet and speak to a small minority of visitors on that day.
- People who vet applications. Some of these will be academics who really don't have a vested interest in who gets a place, because they won't be teaching that course, and others who will only care about teaching.
- the people who respond to emails/phone calls to admissions
I would think the overlap between those groups must be tiny!