> Doesn't seem to add up that at "huge" resolution that PNG would be that small either.

Well maybe not huge huge. Like 1000px wide so they look nice on retina screens.

The key is that these images were just 2 contiguous color areas. Black and transparent. PNG is really good for that because the compression algorithm works on the basis of contiguous color areas.

Was there any attempt to optimize SVG? If it was just a single object/path, it'd be pretty small (if it was optimized/simplified for curves/node count, it could be even smaller), and then it could be harder matching that size with PNG or it wouldn't be that much of a difference.