Elsewhere in the dash we tend to say what format things will be in. I would recommend either changing the button text here and below to add `(csv)` or `as a CSV file`, or add a line of text above the buttons that says something like `The data presented here can also be downloaded as a CSV file. Please select one of the following options to begin the download.`

Also for a large course, would the download take awhile? If so, I'd recommend going with the second option (the text) that adds an additional line indicating that the download could take awhile for a "large" course (define what "large" is - lots of students? lots of problems/sections?)