@Drifter After revising it again I think it's a bit of both really. In the previous chapters they specifilally said that they expect a "Boss" monster that was not on the original request listing from the village
(because the villagers couldn't afford it) but I do think that what they ware referring to is something akin to a pack leader, or an alpha wolf, the term "Boss" may be a bit of a forced term by the author since the setting is a gamelike world. They didn't suspect that the leader would be an advanced species and it
just happened that it was a "Death Wolf", so it's both a boss and a pack leader.
My translation is a bit sloppy but I think I can do better in the future as I gain more expirience in interpreting the context, this was my first time doing this so it was inevitable that I'd make some mistakes.