It’s typically a safe assumption as most of the time when people are talking about voting third party the third party candidate is most similar to the Democrat on the ballot.
But of course if the person wasn’t going to vote if the third party candidate wasn’t on the ballot then their lack of a vote is ensuring that the candidate they like the least has an easier time winning.
It’s obvious from the way they engage with others here, they want you to not vote so trump has an easier time winning.