No, they are not the same thing but they can appear as the same thing on a bow to the uninitiated.
Set is when, as Joe states above, the wood fibers in the belly crushes, as they all do to some degree upon tillering and shooting, which causes the limbs not to spring back to their original position. So you can have set on a bow that was originally, naturally or artifically, reflexed 3" unstrung, meaning the limbs are leaning away from the shooter when held up without it being strung, but after tillering and shooting it holds 1" of reflex. It "took a set" but it does not follow the string. The limb tips are still beyond the riser, or at least in line with the back of the riser.
String Follow is when the limbs of the bow are no longer reflexed or straight but are deflexed toward the shooter. This, too can be a natural or an artifical condition of the bow depending on the stave or the desired design of the bow. Set can cause string follow but some designs and bowers incorporate string follow intentionally as it is said to allow a more forgiving bow. And some bows take a string follow due to the woods used (set taking tendencies) and the the tillering practices of the bower (inexperienced, kind of like m3!).
I hope this helps shed light on it better.
A Glossary of the bower's definition would be a good list to pin to this forum for the benefit of us all.