SVG graphics don't use pixels, they use math to draw lines and shapes in specific places, so when you resize an SVG image you aren't "stretching" the pixels like with a bitmap image, the SVG image is redrawn at a larger scale, because of the lack of pixels the image naturally looks smoother, no jagged edges.
For example take this SVG image of a dragon, you can zoom right in on it without losing any quality, whereas with a bitmap image you would just see a mess of pixels, if you view the source of that image you'll see the SVG magic that generates it.
The browser does not render an SVG image as bitmap.