Yes, I think you are right. Out of curiosity, when I browsed over Coursera's course catalog, most data science related material seems to be taught in Matlab or R (however, there are also others, e.g., Klein's Linear Algebra class in Python). Personally, I think that instructors shouldn't enforce a language requirement. I believe for big platforms such as coursera it shouldn't be to hard to run an respective interpreter to check the code/answer uploaded by a student.