[dagw]

Are there a lot of people who know all about tensors, deep learning, and PyTorch but have no idea what C is?

They probably know what C is in the very general sense, but there are lots and lots of people people who know all the deep learning stuff but have never written a line of C or really understands the when/why you might want to use C and the benefits and limitations of the language. You have to remember that a lot of people currently working in this space don't come from a computer science and programming background and don't have that general background knowledge of computer science.