From the reports nobody was killed, if anything it was just a show of power, that they can hit any target, including those in very close proximity to Iran's nuclear facilities and completely avoid detection.
American news reporting an air strike which is the most likely, Iran have no capacity to detect F35's and the type of strike described looks like a typical precision strike from a aircraft. It may also have been a AGM 158 JASSM stand off missile which the US recently sent to Israel, these are long range, cruise missiles with next to no radar cross section, given the expense of these, it is highly unlikely.