I don't think that explains it. Many Green voters experience some sort of self-hatered, they claim humanity is a disease, etc. In particular many voters do not want nuclear power at all.
They don't want it thanks to decades-long misinformation campaign waged with fossil fuel money.
The Finnish Greens are pro-nuclear, perhaps because they are not beholden to the same sources of funding as their German counterparts (and not to just blame the Greens here: look at your former Chancellor Schroeder).
The Finnish Greens have only been explicitly pro-nuclear, or at least lukewarm toward nuclear as the least bad out of bad solutions, for a few years. This is to a large extent due to a shift of power from the old guard to a STEM-friendly faction inside the party. But less than ten years ago, in 2014, when the then government decided to give a preliminary permission to build another nuclear plant in Finland, the Greens left the coalition govt in protest, as they also did in 2002.