Yes you are correct. That's one meaning of primary. I just think it's misleading by the more colloquial meaning to say "primarily a US company" when AFAIK basically all the engineering happened in the NZ subsidiary of what was initially more-or-less a USA shell company. Engine manufacture was the first thing they moved to the USA that I know of, after one or two launches IIRC.

Aside, Peter Beck has said (probably at a talk I was at in 2014) that they initially designed and built Electron in NZ so that they would be importing restricted technology into the USA, to minimise ITAR problems, which only covers exports.