Well, Giroud's injury was pretty hard to plan for; I mean, how can you possibly prepare for someone being hit by the ball and his leg breaks? Also, Debuchy being out for three months from basically tripping over himself is pretty hard to account for. But, but, Arteta and Ramsey suffering from muscle injuries! They certainly must have been over played after a short pre-season! Eh, no. Full pre-season, RESTED in the CC so they had a full week between games...
Truth is - all those injuries are freak injuries, and Özil seems to have picked up a knock. These things happen in games. We have a few other injuries that possibly could have been prevented, I don't know.
As for Wenger, I can't see myself why he would purposefully lie about recovery time. If there was something to gain from it, why not, but there really is nothing to gain by being misleading here. Most likely, he is just repeating what his medical staff is telling him. My two cents anyway.