I think it’s just a variation on one of his common tropes- take a recognizable situation (Cub Scouts having a picnic outdoors) and then flip the situation around so that the things that usually do the action (eating) are now the subjects receiving the action (being eaten). I think he chose bears to be the ones eating the Cub Scouts because bears live in the woods and also the “cub” in Cub Scouts comes from bear cubs.