Kombucha mold, what was wrong?

Hello, I'm surprised to see that my 4th batch of kombucha grew mold. I'm very confused, since I think I have followed the same steps as my other batches, expect for 2 things:

I removed the 2 older scobys, since they were looking pretty rough. Left the 2 newer ones inside.
I used a combination of japanese green tea (no flavorings or anything, just plain old green tea) and unflavored oolong. In previous batches I used black tea (tippy yunnan).

I see a lot of people using green tea in their kombucha so I don't think it should be a problem... Am I overlooking something?

You probably are overlooking something simple. Like you didn't use enough starter or you touched the scoby with contaminated hands, etc.
I have batches with black, green, and white teas mixed. One right now that is all green and others half black, half green.
Green tea will not make your batch mold. Direct and/or environmental contamination with a low starting pH could definitely get you moldy.