Have you already tried again this strategy? or just this one-time trial and error?. We cannot say this could increase the chance if you didn't test a lot of probability.
I really want him to say or answer this question, and I'm a little doubtful if in the next try he gets the same results in the sense of getting a win like that again, what I'm sure of is that he seems to have only done one try and coincidentally at the same time luck came so that he succeeded in getting that good victory. In fact, it is very difficult to be lucky enough to get such results because this is a game of chance.
Every gambler has their own strategy, but its still a risk. Your friend's silence on finances is telling. It either suggests he's very private or the results arent as great as expected. Gambling involves skill, chance, and superstition.
Im not rejecting your friend's assertion, but be cautious. Never expect a steady income from gambling. Entertainment has highs and lows. Your method of questioning and proof is correct. Great if your friend copies his achievements! Remember: one win doesnt guarantee the following dice roll in gambling.