Disagree. If they ended up not going to college, it couldn't be a "gap year." So it's false by definition. Technically, everyone who takes a "gap year" ends up going to college.
If your question is whether most people who don't begin college immediately after high school, intending to take a gap year, end up not going, I don't have any statistics on that. I expect it's still not true.
I will say that a gap year is not a good idea if you intend to major in math, engineering, physics, or other "mathy" subjects; there's quite a bit of knowledge loss over and entire year of not using math. The same is true in foreign languages (and many colleges require you to take a foreign language), and, to a lesser degree, in other sciences.