There are several things in this picture that suggest it is.
First, it was posted- and almost immediately deleted- by English Olympic sprinter Linford Christie (in the dark shirt).
Second, it’s Puma branded. If you didn’t know, Arsenal have signed a 5 year/£170m deal with the German sportswear company in May of this year.
Third, the shirt is being worn by Thierry Henry and I can’t imagine that he’s going to be asked to wear a fake or prototype kit under any circumstances.
Fourth, it appears that Olivier Giroud is wearing some sort of Puma training top as well.
(The other player is Bacary Sagna who is wearing an Arsenal sweatshirt- brand unknown)
Finally, the presence of three active Arsenal players (and Christie who has been/may still be sponsored by Puma) suggests to me that this photo was taken at some kind of organized event, in which case I doubt that Puma and Arsenal would have allowed the players to appear in anything but the “real deal.”
If it’s real it’s a bit of a departure, but with the right shorts and socks it could work.