I'm surprised that a university setting would have students with this reaction, especially in the UK where people are generally more godless than the US.
Well, 30 years ago I was in college (first time around) and in my philosophy class we debated abortion. It was civil. I do remember 3-4 people having a problem with the discussion, two were being quite vocal (anti-abortion), one was silent and one was on the fence (kept relatively quiet). In other class times we discussed god, reality, proof of existence, etc. Except for abortion, no one expressed offense to other topics -- skepticism, dislike, perhaps, but not offense.
If the sponsor of her lecture identifies as a Christian (and would appear by her remarks that he took offense) and if he knew she was a "vociferous atheist", I do question whether he set her up in advance with people walking out just to make his point.