How would you feel if you were a high profile public servant, terminated without cause, and have the Premier state publicly that you hadn't done any work while in the job (a statement proven to be false)?   

That's defamation by definition...a false statement about someone that damages their reputation.  Horgan's subsequent retraction and apology will mitigate the damages, but it can't/won't "un-ring the bell".

It is not "the end of the world", as you put it, but it is a compensable tort.  The judge's role will be to assess the egregiousness of the statement and determine the damage created by the tort.   It's the judge's opinion hat counts, not your opinion or mine.

But I doubt it will get to trial.  Horgan doesn't want the bad publicity of his mistake being aired out again, nor the financial cost of his mistake known.   That's a lot of political motivation to settle out of court.