Either verb works fine in that sentence. There really isn't much between the two, mix is even used in the oxford definition for blend. I'd say generally, blend implies a more subtle or careful mix, and if you're talking about cooking, mix would probably be the one to use (unless of course, you're putting something in a blender!) But musically, either is perfectly acceptable.
In this very specific context they have different meanings.
blend - the music has elements (which may be melody, rhythm, arrangement, composition, etc) which give it a jazz sound, and elements which give it a pop music sound
mix - the music actually has instruments or tracks which are jazz, and separate instruments or tracks which are pop music, and combines them into a single recording
I agree with Glasguensis that in the music industry there is that technical distinction which useful to know, but agree with Palla that in ordinary conversation or writing where such distinctions perhaps aren't known--or if known aren't desired or applicable--that either verb works fine.