It's a comedy show, but that doesn't mean they don't take facts seriously. As I said in another comment further down, QI is:

a show with a team of good researchers, they can on occasion be wrong (and have corrected themselves for mistakes in previous shows in the past), but they won't put a fact into a show without getting good sources for it

So while they may be wrong in this instance, the fact that they are a comedy show isn't reason enough to think so.