These articles seem more concerned with detailing how important it is that it wasn't Christians. Makes sense for a organization centered around "religion and public life", I guess. Quite the angle.
It's quite important that it wasn't Christians. A large part of the public understanding of history is based on a belief that progress through the early Middle Ages was held back primarily by Christian repression of free thought. There are people who very seriously believe that we'd be flying between stars by now if Christianity had never become predominant.
You don't have to be a Christian apologist to think that it's important for people understand history correctly.
Do people generally think it was Christians? Without looking it up, I would have said "barbarians", which may not rule out Christians but doesn't specify them either.
I think the majority of people have never thought about it one way or the other (and would probably think similarly to you), but there is a substantial group of people who do. While it's by no means predominant, you come across the idea with fair regularity on atheist discussion boards.
You don't have to be a Christian apologist to think that it's important for people understand history correctly.