If you are infamous, you are known for something that is not very good. For instance, a well-know bank robber would be called infamous. The bank robber is famous for robbing banks which is a crime, therefore infamous.
In the case of a grizzly bear, bears are known for being big and scary, and for having sharp teeth and claws. These are not very good. Bears seen as scary are infamous.
On a separate and unrelated note, bears should not be scary. While they SHOULD be left alone, they aren’t nearly as vicious as people claim. A bear attack is most likely less likely to occur than a shark attack (which happens less often than lightning striking people).
