An alternative explanation is the Greens didn't care about nuclear until Gerhard Schröder started to scare them with Fukushima.

That would have been quite a feat of divination. Schroeder was chancellor until 2005 while Fukushima happened in 2011 (during Merkel's government, which actually had pushed the nuclear exit further into the future at first and then rolled back that decision after Fukushima).

The important event was Chernobyl in 1986, from then on it was pretty much clear that Germany would leave nuclear power behind (and this was the Green party's main agenda, and what made them 'big' during the 90's).