Tloewald is saying that if you save vector art at an 8x scale PNG, it will not be 64 times larger. Most pixels in vector art are in contiguous blocks of either solid colors or linear gradients. After prefiltering, both cases reduce to a single value followed by a run of zeroes, which DEFLATE will compress extremely well.

So the only size increase really comes from the edges. In practice, this means that an 8x size increase will often only increase the file size by around 10x.