That doesn't match what I see in the ground. I get 10-20 interns a year on my teams from big state universities and liberal arts schools with CS and stem degrees.
They tend to be awesome. The best ones outperform most of the consultants you find.
Nothing you say relates to IQ stats about the median grad. If CS enrollment was up, it would push the needle I'm sure. It's not. You may as well be saying, "What do you mean most wine is bad? I drink good wine all the time."
Are you also comparing this over a long timeframe? 112 in the 70's -> 100 now means less than 1 point every 3 years. You probably can't notice a difference that small year over year.
That's their hypothesis. So their hypothesis isn't that CS student IQs are dropping.
What does 2017 have to do with IQ?
Actually I think IQ is more relevant now since we have lots of incompetent people holding degrees.