That article seems to be offering legal advice, but from a technical perspective is awful: it throws multiple types of IP law into a blender and then discusses

That article seems to be offering legal advice, but from a technical perspective is awful: it throws multiple types of IP law into a blender and then discusses IP like it's one thing, incorrectly. Of the types mentioned, only trademark must be enforced to preserve one's rights. Both patents and copyright have no such requirement, and Apple's claim here would be copyright-based. In any case, Apple is within their rights to assert that telemoji are an unlicensed derivative work of Apple's emoji, but they aren't compelled to enforce that to keep their copyright.