The short answer is Delgamuukw v British Columbia,  3 SCR 1010, otherwise known as Delgamuukw v The Queen, which is a ruling by the Supreme Court of Canada.
The longer answer is, well, the same as the short answer but with more words.
The decision stems from a 1984 case launched by the leaders of the Gitxsan and Wet'suwet'en First Nations, who took the B.C. provincial government to court to establish jurisdiction over 58,000 square kilometres of land and water in northwest British Columbia.
Fast-forward to this century, when representatives from 20 First Nations -- including the elected chiefs of the Wet'suwet'en -- signed agreements with Coastal GasLink consenting to the project. The pipeline was subsequently approved by the provincial government.
However, some hereditary leaders have not consented to the project, which runs through their territories.
In the Delgamuukw case, Wet'suwet'en hereditary chiefs established that the Indigenous nation has a system of law that predates the days of elected band councils enacted under Canada's Indian Act.
Under traditional Wet'suwet'en law, hereditary chiefs are responsible for decisions regarding ancestral lands.
In the current dispute, some hereditary chiefs say the decision to approve a pipeline in their ancestral lands without consent is an infringement of their Aboriginal title and rights.
So... yes, it's pretty complex, as far as such things go. But the very short answer to the title question is "The Supreme Court of Canada said they're different."