I don't think that was the implication. The original post just said that the democrats and independents split the vote (spoiler effect). There was no implication as to which was the spoiler.
It's not a "spoiler effect"; maybe a split constituency is a better term. Spoiler implies that somebody has something, and someone else steps in and ruins it. These are all equal people running for the same office.
If anyone is a spoiler, it must be the Democratic candidate.
Your reasoning may be well-intentioned, but it is yet more 3rd-party-blaming.