Do you have a link? I can't find one with these searches:
https://duck.com/?q=site%3Afoxnews.com+david+hogg+paid+actor
https://duck.com/?q=site%3Afoxnews.com+david+hogg+crisis+act...
https://duck.com/?q=site%3Afoxnews.com+david+hogg+antifa
I know some crazy people said things like that, but I can't find any evidence that Fox News did.
They did so with no evidence, even though the accusation is far more specific and easily testable than it is in the Covington case. And even after being called out on it, they continued to repeat the smear against better knowledge. The difference is as clear as night & day.