I once went to see Billy Dee Williams speak to a group of college acting classes. Many of the questions posed to him were kind of...odd, largely exercise-related: "Do you still work out?" to which he answered "I try to get to the gym once in awhile, yeah," with a mildly puzzled expression. As the Q and A progressed it became clear that many, if not the majority of the students in attendance believed him to be Carl Weathers. It was embarrassing, although I don't think Billy Dee ever really caught on.
To be extremely nice to the girl, these days they do look somewhat similar, and if she had only just seen American Beauty and didn't know who was in it, and had only just met Cusack for the first time, I can see how she could think he was the same actor.
Of course that only makes sense if it's normal for an interviewer to not do even cursory research on the subject they're interviewing, and it also doesn't excuse her for insisting that yes he was in the movie when hopefully he would know what Oscar-winning films he's starred in.