It’s actually not entirely true, it only counts stein as the only 3rd party (the libertarian candidate in PA got 3x as many votes as her, I’d bet those 3rd party votes wouldn’t have gone to Clinton) AND doesn’t report factual numbers.
It’s just not true.
That said unfortunately voting for a 3rd party candidate is largely useless in the USA and the forces trying to get their opponents voters to vote 3rd party are probably more overwhelming then the forces actually compelling folks to vote 3rd party.