Most immobilizers are lazily installed. If you don't do it right, they can still be started. A lot of them are installed really close to the barrell so it's easy to bypass further down, especially in the case of ours and a lot of other cars that have a plug further down than the immobilizer cuts. Our cars also have 2 ignition wires, one runs the motor etc and the other is for fans etc. Cut the wrong one and the car can still start. Most installers also cut the ignition and starter, which is only really effective on an automatic car, as a manual can be push started if you can bypass the ignition. I generally try to always cut ignition and fuel, so the car will still crank but not start. I'm pretty sure I cut the pump or ECU off the back of the relay panel behind the dash in mine... but it's been that long I don't remember.
Working in the industry I see a lot of this dodgy shit all the time, people are just too lazy or maybe they don't have a clue. I usually try to rectify the issues and make sure an immobilizer/alarm actually does it's job and also can't just be found/pulled out without even removing the dash.
Also, a great feature on the autowatch 446 premuim's is the anti-hijack. Even if you take the keys, in ~45sec you get warning beeps 3 times, then the alarm goes off and the alarm cuts the immobilized points in pulses bringing the car to a stop. You just hide a button somewhere in the car and if you don't press it in the window you have before the alarm goes off it will do the above. Also does the same if you get hijacked... senses the drivers door opened (has to be set up right) and has the same effect as above. Once you enable it, it's easily switched on and off for those times you need to take it to the tyre/panel/mechanics place so they can start it with no issues and you don't have to tell anyone about the secret button.
GL with the car mate, scum should be burnt alive.