That would appear to be a thermal efficiency chart, which does indeed have the same shape as a BSFC chart.
Toyota claim a peak thermal efficiency of 40% for one version of this engine and 41% for the other. I suspect that chart is for the 40% version.
They have actually chopped quite a bit of the the top of the curve as the 40% version has a peak torque of 205 Nm at 4800 rpm whereas that thermal efficiency chart is only showing a peak value of approx 155 Nm.
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