I know you are correct about grammar when it comes to among and between. However, grammar is always changing and evolving. English is a big tent that way. When I was in collage pursuing my math degree, I started mentally changing prove something to show something since show had a softer and easier connotation than the stricter prove something. I got far beyond the need to do that as I progressed. However, I continued to do so as habit. You could simply make a conscious effort to change the grammar and go ahead and solve the puzzle. Some things will probably not change. So, just work around it and be at peace with them.