on a quick google search, it says forest fires can cause clouds that rain, but it can also cause clouds that just have lightning and cause more fires. i kind of doubt 1 bonfire is enough to affect the weather.
also the premise of this series is a little meh, guy is spending money on strangers because he saw a pretty girl? spent 5 million + 5 million yen on the water wheel, which is like ~100 thousand dollars, 0.25% of his winnings. So he can do something like this 400x before he uses up his 4 billion yen. maybe the plot will get more interesting.