"If normal practice was to run things through approval before publishing and he swerved it in this case then he is rightfully sacked."
Okay, but if seeking approval prior to publishing is required (rather than just a courtesy) then one can infer that Lynn was in the practice of doing this simply due to the fact that this didn't happen earlier.
Which raises the question: why did he (Lynn) deviate from past practice in this one specific instance? The clear answer is that he believed that, had he sought approval from Slaughter, there was a strong chance that he would have had to censor his piece.
Whether that censorship would have happened or not is up for debate but it is clear that Lynn was sufficiently convinced that it would - so convinced that he was willing to risk his job.
The other question that comes up is: why was the response so absolute from Slaughter? She claims that she wouldn't have censored the piece, which implies that the content was not inaccurate, misleading or in breach of their guidelines. So why terminate the relationship over a single* lapse in procedure?
Take a hypothetical parallel - a company employee commenting publicly via social media. Let's say a company is celebrating 5 years in business and a social media drone posts a tweet or whatever saying how proud the team are to be celebrating their 5th anniversary of selling high-quality widgets but, crucially, that drone doesn't get the required approval of the marketing manager before posting.
A response is needed, surely, to re-enforce that all staff must have public statements approved but nothing in the post would have violated any content rules and certainly would have been approved.
In such a situation, is it reasonable to fire someone for that?
Bringing it back to this case, the real test would be what the consequences would have been had Lynn done the same thing (in not seeking approval) but had published a piece that was supportive of Google and their interests.
For Slaughter to be believed, it must be shown that Lynn would have been let go in that situation, too.
* - One can strongly infer that this was an isolated incident and not a pattern as Slaughter would certainly have mentioned this history, painting it as the proverbial last straw. Had that been the case.