What I know is that what could be applied to hockey and other sports games could also be applicable to soccer betting as well, which is why I commend you on testing this out. However, this strategy looks odd and it shows some kind of "gambling within gambling" kind of pattern which I am not particularly comfortable with. The best way to bet on sports is to know the full information about the two teams playing and use your discretion and instinct to make your bet. This is still subject to some luck factors as well, and not about a certain pattern that your friend taught you.
Besides, if a team can score a goal and could keep it till the end of the match often, it only means that the team is not weak but strong which is a factor that will reduce the odds of that team against the other. This is never to my advantage and I do not do small odds in my sports betting which has been one of the ways to help me manage my gambling activities well and not be wasting my time like so many people do it randomly.
In other words, this style's risk is too high for me.
Gambling within gambling pattern is always the kind of system done in most strategies even the martingale system which one can apply also in this strategy. and just like @Solosanz said, this is like betting on your favorite team but just multi-betting but this time doing it live and in the 2nd half, and at the same time you are almost sure the team will win because they already scored.
And you do not think that the "gambling within gambling" approach is such that can increase the risk of the gambler? As we are looking for a means to reduce risk, you are here advocating more risk, that's certainly not conservative. Just like the martingale approach you mentioned, it is such that puts the account of the gambler at a higher risk and martingale has never been a term in any risky activity to denote something done with ease but it always denotes something done in desperation. Are you now preaching desperation in gambling which we always advised against?
As for the betting style, this is not just a good style that denote good and careful speculation but gambling on a certain pattern. Mind you, who says since a team has scored, it has now guaranteed their winning? This is baseless and your argument is not just constructive in this regard, histories would prove you wrong millions of times.
Based on my experience, it doesn't work much in the very popular premier leagues or on FIFA because of the chances of DRAWs.
Oh, nice that you know it doesn't work in the EPL. But I do not know what you mean by "FIFA" because that name is the entire football body which the guy claimed he is using the strategy for. So I don't even know if you are For or Against anymore.