They did an interview with the guys from NYT's Hard Fork (https://podcasts.apple.com/us/podcast/hard-fork/id1528594034...).
When asked what their act of protest was against, they said "cars in general." They're very anti-car and, although they acknowledge that self-driving cars will be much safer in the long term and could transform a world full of wasteful single-car ownership, they are adamant that cars shouldn't exist.
Yes, they're in their 20s and enjoy riding their bikes in San Francisco.