What gives you the idea that any of this happened because of a mistake?
The articles and discussions at un-named leftist sites, sites who are responsible for digging for Jeff's "trash" are not concerned with a "mistake." They are concerned because someone was allowed to ask questions during WH press briefings that didn't jibe with usual accusatory questioning. They were concerned because Jeff doesn't have "journalistic credentials" and clearly describes himself as conservative.
I have no idea where you are getting that some "mistake" caused this.
The mistake in question was treating something that Rush said regarding a "soup line" quote from Harry Reid without fact-checking it.
Regarding the rest of the story about Gannon, I will wait to see what shakes out.