Well in abstract there are plenty of possible spaces where a set can be bounded but its boundary does not exist within the set (e.g. consider the transcendental

Well in abstract there are plenty of possible spaces where a set can be bounded but its boundary does not exist within the set (e.g. consider the transcendentals between 0 and 1) so talking about the "hull" as a boundary is completely useless. Even so, picking the word "hull" was perhaps careless. A lot of people, even mathematicians, are confused on the definition of circle vs. sphere (the circle is the boundary, the sphere is the volume), so even if you use these terms "correctly" you probably want to define your understanding of them.