What it also doesn't explain there is that many plant seeds are coated in an oil or ichor, which prevents them from germinating when the ground is dry, otherwise they would sprout and die. When it rains, this oil is washed away and mixes with chemicals in the soil to produce petrichor. And then it is safe for the seeds to grow!Here's the science behind it-
http://www.livescience.com/49520-smell-of-rain-aerosols.html