But it's not any specific facet of their form that distinguishes it from communicating an idea vs something physical about the represented object -- it's the context and the intended message. Nobody puts a butterfly decoration on a pillow to say "there's an actual butterfly on the pillow," or say something about that butterfly's physical disposition. They're using the idea of a butterfly, generically, to evoke appreciation for the intricate beauty in natural patterns, life, warm months, spring, symmetry, insects, and/or any other connotation inherent to butterflies which will probably change based on the context and specific representation. When deployed for communication tasks like that-- as emoji are-- they need to evoke the idea of something rather than portraying an actual instance of that thing, so having an immediately recognizable form, most importantly its profile or silhouette, is far more important than physical accuracy. In fact, physical accuracy often requires more visual complexity, increasing the cognitive load to parse it, which makes it worse at its actual job for little to no benefit.
Even heavily abstracted symbols may need to communicate a specific physical disposition. Consider the door-open indicator on a car. It's not a physically accurate-- it doesn't need to portray anything except "this is a car, this door is open"-- and it would probably be less effective if it tried to be. But since the physical disposition of the door is important and you're not just evoking the idea of a car, it must be included.
For illustrating stories about a butterfly, or using a photo to reference a butterfly doing something specific, or trying to illustrate something else about the physicality of butterflies, then sure... that physical accuracy is important. But the author doesn't make, or even seem to understand that distinction.
Yeah, semiotics is a pretty neat topic even if the available literature skews dense. How well a designer wields those concepts to solve communication problems without words is one of the things that distinguish novices from juniors, and juniors from art directors.