Some people believe what ever the people in charge tell them. It is a mind set that is fostered from birth in some countries, sadly it has been so in the USA now for about 40 years. Our kids are told to believe what ever the government tells them. I would imagine this woman and who ever else was out there swimming simply took the word of the people in charge that the sharks were all gone.
It is sad. . .people 'do' believe; and tend not to question. One can find oneself - or lose oneself - simply because a sign was mis/displaced; or warning coulda/shoulda/woulda been there/.
We really must be 'self-reliant' and have the gifts of critical thinking. Certainly, a virtue that is NOT being taught/shared these days at least 'at large' in Liberal Land. . .