So that would imply there is a 3rd channel of FADEC, if the EBCAU is able to control the throttle valve electronically when both lanes of FADEC have failed then it seems to be a triplex rather than duplex system.
I presume the throttle response in EBCAU mode is significantly damped to encourage smooth collective inputs and avoid rapid Nf changes.
I think other systems would just freeze the throttle valve in the event of a double channel FADEC failure.