Oh Snow Leopard, you have made my day. Remember when updates used to be in the hundreds of megabytes? Your unified architecture has slimmed down apps and updates so much that they are only a thousandth the size now.
Or it could be that it’s just a tiny patch to fix an uncommon but problematic hard drive error (since it’s only 22KB more for Leopard). Either way, the update is there. Been having hard drive issues? This may just fix it.