SLS isn't that toxic, its just overly an effective surfactant that strips all the natural oils from your skin/cheeks. Its why your hands free dry when you wash dishes with dish soap. Also strong enough to remove crude oil from birds.
Your parent poster was well aware of that, and also assumed his parent was aware of that as well. His post was a subtle version of "arsenic can't be 'organic' because cannot be composed of carbon chains because it is an element which is not carbon."
The advantage of his version (especially in spoken conversation) is that you can tell someone they are wrong, and typically if they have such a gross misunderstanding, it will go completely over their heads, and they won't realize that you are telling them they are wrong.
Water is considered an important part of organic chemistry by everyone, but pedantic chemists. Original poster may have been thinking of cyanide but As is often found in plants and animals and is not man made. Which fits the casual definition.
