I’ve been following this via another news source and the situation is a mess. Basically, when Great Britain declared sovereignty over British Columbia in 1846, it never signed treaties with the native people in the region, and so they technically never surrendered their land rights. But that didn’t stop governments from handing parcels of land to settlers, municipalities, and federal agencies anyway, which built a new property system right on top of the old one. Because government proclamations carry official weight the court allows that land acknowledgment exercises (often heard here in the U.S. at academic venues) that mention “unceded” lands could carry legal weight.
Here in the U.S. we (luckily) managed to avoid this by recognizing tribal governments existed and getting them (usually by force) to cede lands in exchange for money, goods, and or reservations. Not exactly nice, but theoretically legal.