That's not really unusual. I used to work there before starting my current job about a year ago. A couple of months before I left, we had such a threat. Other than staff, no one even knew it had happened.
Hospitals are a different animal when it comes to thing like bomb threats and fires. The information tends to be played close to the vest, and employees are taught to stay in place even when a fire alarm is going off. It tends to rattle patients and visitors some, but employees are pretty used to it. They drill for things like this, and for things like kidnappings almost constantly.