I'm assuming you are referring to the killing of 402 by 469? that was actually a very, very weird incident. i'm not sure we will ever understand why it happened. i wouldn't expect it to be food-shortage related, since it happened so late in the season, but it might've been. if it was, it didn't provide 469 very much food, because he was quickly forced off of the body by 32 Chunk.

brown bears killing other brown bears is very, very rare, so even with the lack of salmon that year, it was a very strange event. also, just as a note, 469 had been found with a bear corpse before, though we don't know how he acquired it. If he did kill that previous bear, then he might just have been particularly prone to killing other bears.