premise: Mark Arm (born Mark Thomas McLaughlin, February 21, 1962) is the vocalist for the grunge band Mudhoney. His former group, Green River, is one of the first grunge bands, along with Malfunkshun, Soundgarden, Skin Yard, the U-Men, and others. He is also the manager of the Sub Pop warehouse and previously worked at Fantagraphics Books.
hypothesis: Green River was founded before Soundgarden.
reason: The context lists both bands as being among the first grunge bands, but doesn't specify which came first. I think that the system had trouble with this because there was no definite timeline in the context.