Of course its a public comment if you plaster it on a public forum about a company you work for! As an employee, company confidentality is part of your contract. Break that, especially if it's negative or a rumour that is negative, you are asking for trouble if caught (and companies/managers do browse these boards!)
Must admit, I've learned my lesson with a couple of close shaves and lost a job offer cos of comments on another forum, because somebody else told a manager who I was..