I thought using an unintended method was considered bug abusing?
It's not unintended method, it's unintended design balancing.
There's always a risk when working with 22 years of content relevant to a new Skill that we can miss older content methods that are outside our intentions for the XP balance of the skill. There was nothing wrong being done by doing this.
Essentially it was a nice find, but something we wanted to close off for balance reasons rather than being a bug that was abused.