While technically it would probably fit the definition, usually what's meant by steganography regarding images is hiding the data within the image itself (using differences in pixel values that are not easy to spot). As far as I understand it, this just makes use of the file structure. It's beyond me though how it survives twitter thumbnailer. I would assume that one of its purposes is to strip any unnecessary metadata from the image, making it as small as possible.

The easiest implementation would be to use the 2 least significant bits in the blue channel, and the least significant bit of the red channel, to encode your data payload. Just sticking the data in the metadata portions of an image file seems like hiding behind the only bush in an otherwise featureless field. ("Reginald Maudlin, will you stand up, please?")