If 10 people vote and 5 go to Trump and 5 go to biden then you’ve avoided a Trump victory and allow for another round.
If in that 2nd round a person who voted for biden decides to go 3rd party now trump has 5 votes biden has 4 and the 3rd party has 1.
The person who switched to 3rd party helped Trump win along with the 5 who voted Trump. If you don’t understand that then you’re being purposefully obtuse. Or you could explain how that 3rd party vote didn’t help Trump without responding with a thought terminating cliche