It wasn't me, but I can imagine how it was done.
Hook up a bunch of sensors to an arduino, throttle, injector pulse, rpm, speed sensor, map sensor, maf, temp, etc.
Hook up a $5 bluethooth to uart adapter on the arduino
Emulate an obd protocol on the arduino (look at how
elm does it maybe), basically wait for commands (pids) on the rx port via bluetooth, and give responses via the tx port, each pid can be a single reading or whatever combination of sensors morphed into a number makes sense.
pair your android with the bluetooth, install torque, and add any
custom pids to torque that you need.
add gauges to your torque screen for those pids (which represent readings from the arduino)