The cng diesel fumigation is well known technology and there is no "magic" in it. You simply feed (metered by different devices) cng low pressure into intake before turbo, then cng air mix pushed into cylinder (by turbo). When mix compressed by piston it is "waiting" for ignitor (diesel injection) then this all air/cng/diesel mix "explodes". Cng adds 30-50% extra power, so you simply ease off your gas pedal and as soon as you do this you diesel injection amount lowers.
Diesel engine has no throttle (most of them). Your gas pedal is "attached" to fuel metering device.
In gas vehicle your gas pedal is "attached" to air metering device which in turn "attached" to fuel metering device.
Don't look at cng as an air "thief". It works instead of diesel
Just watch this and see power it gives: