I don't think that's the definition usually used for "independent" when talking about voter affiliation. US politics has a long history of people telling pollsters (and filling out voter affiliation info in actual elections) that they aren't affiliated with a specific party because political parties have generally historically been seen pretty negatively in the US. In reality, many of these self-identified "independent" voters have voting records that are heavily skewed (if not straight-ticket) to one party or another. I don't have actual numbers on what % of independents this is (I too am interested in the parent's question on this matter), but it's definitely not a "definitionally, none" answer.
I'd argue that voting predominantly for one party or another doesn't identify the unaffiliated individual as a member of the party who's candidates they vote for. It absolutely doesn't identify the whole unaffiliated voting block as having any secret party affiliation. Telling the whole party system to take a hike is an active choice and it happens in counties that only allow a single political party as often as it happens in countries like the US where there are only really two choices.
