I dunno if that's true either. Things like UBI were wacky ideas popular in SV culture long before their recent mainstreaming. I think the libertarian streak is better described as a mistrust/realism (depending in your views) of the _competency_ of any given government program.
The government's advantage is that it lets us directly align objectives in a way that markets often don't, but it's disadvantage is that it'll generally optimize much less efficiently for the objective it's targeting. This means that government action and markets are appropriate in different situations; I'm not crazy about the fact that we're the least competent at transit construction in the developed world, but I'm still a supporter of transit investment despite the eye-popping levels of waste.
Live in San Francisco long enough, and you get a really strong sense of how detached a government can get from reality, and how much its actions can reflect the selfishness and idiocy of part of its constituency instead of any pretense of benefiting society or achieving its goals. It's unsurprising that you'd see a portion of the population, especially one used to more well- functioning institutions, start to drift towards support of government policy that doesn't rely on individuals within govt making complex decisions. UBI and other such hands-off policies fit directly into this. They're not anti-govt spending, they're anti-centralized decision-making