Even when games use rectangular hitboxes, they often use multiple of them to make characters' moves assume desirable shapes. On the other hand, nothing stops you from shaping your "freestyle" hitbox any way you want intentionally.
If something happens unintentionally, it's a matter of questionable effort at game designing rather than generic shape of hitboxes or something. Alternatively, it may be a case of writing off something you don't like as "unintentional", "shouldn't be a thing" or whatever, even if the thing in question is designed to work that way.
Tl;dr: "Fuck Cat's b3" would be much more laconic way of writing that original post.