The whole point of living soil is to give your plant certain nutrients at certain intervals, releasing over time, not all at once.One easy way to tell that this is bs is to pour a bit of synthetic nutrient solution into a cup and leave it out. You'll notice bacteria growing on it pretty quick.
So yeah if you randomly add concentrated synthetic liquid nutrient to your plant you're going to kill it
One easy way to tell if that guy's bs is if you read his last post