She studied math early on, so she's definitively technical. She is the CTO, so she kinda needs to balance the managerial while having enough understanding of the underlying technical.
Again, it's easy to be a CTO for a startup. You just have to be at the right time. Your role is literally is, do all the stuff Researchers/Engineers have to deal with. Do you really think Mira set the technical agenda, architecture for OpenAI?
It's a pity that HN crowd doesn't go one-level deep and truly understand on first principles