Saying that a 20x20 image of a Twitter logo is 4000 bytes is just so wrong.

The image is of a monochrome logo with anti-aliased edges. Due to being a simple filled geometric shape, it could compress well with RLE, ZIP compression, or even predictors. It could even be represented as vector drawing commands (LineTo, CurveTo, etc...).

In a 1-bit-per-pixel format, a 20x20 image ends up as 400 bits (50 bytes).