These students are high school students. I'm very doubtful that this course covered material like file types and encoding. First year CS classes are almost exclusively programming basics and architecture.

This line of thinking only really makes sense if you presuppose that every person taking a computer science course in high school has an understanding of file types. Many don't have this knowledge. I don't see why students should need to have additional knowledge that is outside the scope of a course, just to pass the clase.

There's a reason these things are taught in a CS program, often at higher levels. And that's because they're not common knowledge.