Again, sea lion safety is not common knowledge. They're not self-evidently dangerous like a snake or a wolf. Few city dwellers have ever encountered one in the wild. Why would a random tourist be expected to know that it's in a sea lion's nature to jump out of the water and try to carry off a person?
What I find interesting is that the head of the port authority, whose literal job it is to keep the public informed about safety at the harbor, didn't think it was necessary to post warning signs till after the attack. And in doing so, made disparaging remarks in the media about the victims of the attack who nearly lost their daughter. Perhaps if he wasn't wrongly assuming that this stuff was common knowledge, he wouldn't have to be talking about tourists nearly dying in his harbor.