I think it actually stems from that famous Chinese brick set for kids which was supposed to teach the alphabet, where the Chinese confused the letter З with the letter Э, and wrote АРБУЭ instead of АРБУЗ (watermelon); the ending -БУЭ is a bit funny because it sounds like a vomit sound, so it became popular on the Internet to attach -УЭ or -Э to the end of words, I think this is why people write котэ instead of кот.