It is officially released, just not for Linux/SteamOS. But if you buy it for Windows, you get access to the Linux/Mac files through Steam. I think Bohemia Interactive are waiting for VP to bring the Linux/Mac versions current to the Windows one before they make it official. Hopefully that will happen pretty soon. You may want to respond and ask them when they will be at 1.64. They have battle eye so it's almost there.

I know that ARMA 3 are released for Windows, but I think that Virtual Programming should not publish a game trailer if they don't release it

It is a very unusual situation. Like I said, hopefully they get it up to date with the Windows version and it becomes an official port. I'm pretty sure the reason Bohemia hasn't made it official is that the vast majority of servers will only let you on if you're on the current Windows version. If they made it an official port and sold it as such, right now a lot of people could buy it and complain that they can't play on popular servers. Making it an official port right now would make Bohemia look bad.

I'm confident though as Battle Eye was supposed to be the biggest hurdle, and that has already been overcome.