If two trains are both traveling in opposite directions at the speed of light they both get there in no time at all.

I'm curious how they teach math in all of those countries who outscore us in math and science. I can't help but wonder if this experiment shows that people struggle to actually apply abstract concepts.

Dme,
One teaching method for math that we don't use here is the mastery method. Most schools and even homeschool textbooks teach math in a spiraling fashion, quickly covering many areas of math without the depth necessary for students to completely master the basics.
This is why math curricula from grades 3-7 teach pretty much the same things year after year.
I struggled with math during elementary school, but as soon as I got into algebra, I found that to be much easier.