That number sounded really high to me and I went looking for information to refute it. Turns out 50% may be a rather modest estimate today:
Foreign Students and Graduate STEM Enrollment https://www.insidehighered.com/quicktakes/2017/10/11/foreign...
> The report found 81 percent of full-time graduate students in electrical and petroleum engineering programs at U.S. universities are international students, and 79 percent in computer science are.
The Disappearing American Grad Student https://www.nytimes.com/2017/11/03/education/edlife/american...
> The dearth of Americans is even more pronounced in hot STEM fields like computer science, which serve as talent pipelines for the likes of Google, Amazon, Facebook and Microsoft: About 64 percent of doctoral candidates and almost 68 percent in master’s programs last year were international students, according to an annual survey of American and Canadian universities by the Computing Research Association.