This is one of those statements that could be technically accurate yet it must be put in the proper context.

The FBI is an organization of professional who operate at lightning speed. So, of course the agents working the case didn't need to spend too much time on the investigation. After all, they are experts.

The media on the other hand are bumbling fools who get things wrong all the time. It's only natural that they would take much time to do their own 'investigation' of the Melania speech issue.