That's not how statistics work. https://en.wikipedia.org/wiki/Sampling_(statistics)
Yes, it is. It is simple logic. If you only test patients that are at a high risk of dying from the virus then, of course, the percentage is going to be higher than if every single person was tested. We have no idea how many actual cases of Coronavirus have been or are in the U.S. but it is way higher than the number of people who've been tested.