As a IRC-chatting teenager in the mid-90s, I am somewhat an expert in emoticons and can’t possibly imagine a world where emojis didn't exist.
But I m surprised no one mentions the “!” or other stylistic tools like all caps. These are “contextual modifiers” for text that have existed for ages. Some languages do have sarcasm punctuation and possibly small adverbs that annotate some kind of emotional state.
So basically yes, the article is right, emojis work mostly like words, but for me it’s just a continuation of what existed before (punctuation and onomatopoeia), and its extension and spread was made possible by the technology (an imposed vocabulary and convenient keyboard).