You have no idea if this works or not just because he says it does. Who is he? What is his biilogical knowledge? The fish might all be dead now for all anyone knows.
Soil creates ammonia for up to six months. Fish can be killed. Most soil aquarist sources recommend a dry start, for six months. The soil has no benefit after a year, and the only--I repeat, only--benefit to soil is the initial influx of CO2. But the plants do not need this anyway. I have set up dozens of tanks in my 30 years, never lost a fish.
There is so much inaccurate and misleading "information" in this hobby, thanks to the internet, that it is mind boggling. You cannot believe a word of it.