Emirates Stadium capacity: 58,967
Arsenal v Man City attendance: '58,420'
Number of empty seats: around 20,000
Seems legit...
I think it's against the FA rules and general stadium safety guidelines to bullshit your attendance by counting non-attendees in the total count especially when your ground gets its data supposedly from turnstile clicks. There was definitely no more than 40k there last night if that and it most certainly was Arsenal's lowest turnout in that stadium and probably no bigger than a maxed out Highbury.
Anyhow, AFTV is gold right now!