No you don’t need a license to be a journalist.
My thought was more about the scale of the project. For a journalists, just fact checking someone online doesn’t make you a journalists. If you went out to fact check something at the source, compiled a bunch of evidence and presented it publicly, then you’d call your self a journalist.
Back to the electrician (ignoring license requirements), swapping out a light switch isn’t much, but if you learned how to rewired a whole house, install panels, ceilings fans, etc - you’d call you self an electrition.
And you’re right, the electrician is kind of a bad comparison.
Why are they not scientists? Sure their profession was in special effects, but you don’t need a degree or a lab to carry out scientific research.