Not necessarily full throttle, more likely 75% or thereabouts. At full throttle, many automotive engines use a extra rich fuel mixture for maximum power, extra cooling, and to prevent detonation.
Be being programmed to go to a rich fuel air mix during those brief full power bursts, the compression ratios can be higher allowing for higher efficiency during part throttle cruise where the engine spends most of its time.
In this chart, this particular engine has a lower specific fuel consumption at half throttle up to about 3500 rpm, above that, the half throttle specific fuel consumption is higher than full throttle, as the pumping losses increase with higher rpms.