Oh, wait. It's one thing to request a nonexistent page; it's an entirely different thing if your analytics program says they were actually on a nonexistent page.*
But that's a heck of a lot of clicks for the amount of time given. A person might hop around 2 or 3 pages, spending 5-10 seconds on each before leaving the site-- but 279 pages at that rate? Nuh-uh. That's a slow robot. Did they pick up associated files such as images and stylesheets? Look at the exact timing in logs. Some robots do get all files, but their timing is different from a human.