If I was doing a fire alarm system I would get one of my trade partners to do it that's had the appropriate training has the right test kit and insurance. That is despite having knowledge to do the job, in reality I would become a skivvy to my trained trade partner(subby) and the trained person sign it off. (I dont do fire)
Think the devil is in the questions, it was advised it should be in fire cable at no point did he say it was okay to wire it in alarm cable.
The question asked was could it be wired in alarm cable, the answer is yes, not that it is okay to do so as you were already advised it should be in fire cable.
I can see how the misunderstanding has come about.
we have certainly connected a few intruder panels to fire panels by the cable the fire engineer has left for us, so it can be recorded on the alarm panel and use one communications device.
The process is the same, its an output or relay from the fire panel into a zone in the alarm panel programmed as fire, often have two communication devices, ip based (apps and notification) and gsm based nowadays but dials a series of numbers as well as sending texts to them all.