Hands up if you thought that said syfy.com and you were surprised
150 million page views a month works out to 57.9 pageviews a second. So the vast majority of those requests must be JS, CSS, and static image requests, although 98.5% seems a bit off?
The 3900 requests per second are likely not constant. That number is probably during their busiest time during the day, so their infrastructure needs to support that kind of traffic. You're right, though, requests per second likely includes all file types.
Read the comments section as well. The author (Ramki) has responded to queries raised in that comment section.
From the comments, those are 'backend requests' and not even static file requests.