A raster image, such as this one (PNG), is composed of thousands of pixels, each assigned their own color. If resized, it loses quality; you cannot add data that doesn't exist. A vector image is composed of shapes formed via mathematical equations, and can be easily resized.
What the person wanted to do is vector your image; basically, trace over it in a vector program, producing a vector image. Then he/she could use that vector image to make a huge image, much larger than yours.