Cheating is deliberate. This was not deliberate.
Yes, most (if not all people) accept that it was not deliberate, but "cheating" does not have to be deliberate.
Think of a sportsperson accidentally taking a drug that is on the banned list - eg. Shane Warne with the diuretic, or the Essendon players (if they did actually take what the authorities thought they did), etc. They didn't act "deliberately" to gain an advantage, but it's still cheating.
Regarding Seb's comments, there were other players commenting about the 19th man, but the worst part of it (which was missed by some media outlets) was mentioning the 31-17 free kick count and suggesting that the umpiring was rigged.
A 3-match ban might be right if maybe a little harsh, but comparing that to NA's 2-match penalty and fine (that was recouped just by playing in the GF) for actually "cheating", it might be considered laughable by some.