Ok maybe my original statement was too strong. You do need some linear algebra to proceed through calc III as Unknot notes, and the two are tied together, as dx notes. But, in my experience, the concepts from linear algebra used often in calc III, like the determinent, were explained in calc III. If you had taken linear algebra, you understood it that much better, but if not, a little self-study was usually sufficient to grasp the concepts that you missed from linear algebra.
I don't know if this is how most linear algebra classes are, but mine was mostly matrix manipulation, uses to create 3D objects, eigenvalues, and subspaces (And all concepts contained within them). There was quite an emphasis was on proofs, and pretty much none of that knowledge was drawn upon in Calc III.
Just a style of teaching the two courses, maybe?