I know I'm being a bit repetative, but I'm still strugling to understand why people are blaming the Principal for anything? If my boss had a question about something in my area of expertise, I would really, really hope he'd actually ASK ME instead of googling it.
Sure, the Principal could find the plot out online, but that's almost certainly NOT what he was most interested in. Instead, he wanted to know (or at least should have wanted to know) how the book furthered the goals of his English department, and how his teachers used the book in their classes. To understand that information, he'd need to know not just the actual plot, but also the plot and thesis AS INTERPRETED BY HIS TEACHERS. Nothing on google would have given him that information.
It sounds to me like he went to the experts on the subject instead of being lazy and googling.