Theo is playing really well. He is making passes now he wouldn't normally make, he realizes he has more time. That one pass to Alexis in the first half which the latter hit over the bar was great bit of awareness.
I think we really tend to ignore the extent of damage sporadic injuries can do to a player's game in the short term.
Theo had started playing the no. 9 role exceedingly well before Wenger brought him on for the League Cup game and he got injured. Why we get so many injuries or hoard injury prone players in another subject.