Yes, there really was a curse on the tomb of Tutankhamen, because many individuals got sick after visiting the tomb. However, this may have been explained by bacteria and other health risks present in the tomb, that may have called health problems. Even so, the people who visited the tomb suffered for having disrupted the tomb, so it could be said there was a curse.
Curses don't exist, in the case of Tutankhamen's Tomb or anything else. It's not the explanation of anything that may have occurred, it's a perceived force that there is nothing to indicate actually exists and is simply used when people don't have a realistic explanation for something that took place.