So he doesn't know how to configure nginx, or the db. So what? It's already running. Database skills are fairly important (since they are your bottleneck), and it's important to have some internet knowledge (to prevent security breaches), but if a startup is hiring it should already have the stack in place. The big advantage of a "starup generalist" is they have probably played with a few different stacks, and know which one to pick, but it's too late for that.

And big company people know all the stupid mistakes that big companies do, and can help warn you about them as you grow.