He's not. Binvis isn't going to tell you if there's steganographic content. He's not showing us the output of a steganography detector like Pixelknot / stegdetect. In his example with the blue blob, if there was steganographic content in that space it wouldn't be solid. It's also easy to figure out if there's an added trailer or not (you can append any extra data you want to the end of an image or ZIP file), but he hasn't done so.
He's not. Binvis isn't going to tell you if there's steganographic content. He's not showing us the output of a steganography detector like Pixelknot / stegdetect. In his example with the blue blob, if there was steganographic content in that space it wouldn't be solid. It's also easy to figure out if there's an added trailer or not (you can append any extra data you want to the end of an image or ZIP file), but he hasn't done so.
Because clearly they know less than they proclaim