Is it okay to store bamboo flooring in the garage before installation?
Unless you live in a climate where you basically have your windows open most of the time and there is no heat or air conditioning then your flooring needs to be in your house 2-4 weeks (differs by wood type and climate).  

So given your conditioned space in San Fran I would say that you need to move it in.  The wood needs to be in a close approximation to the installed environment.  

I don't know your installer but I would be highly highly skeptical of his knowledge and abilities given the advise.  This is flooring 101.