I think that's probably true, but depending on how unlikely, we still expect a core group of people who do consistently apply that ability.
Either way, we're talking about whether or not the NYT headlines have been biased against Sanders, an empirical question for which the data set is readily available---it doesn't really matter if most people's impression is correct.
@Jack V Savage To show that "the mission" of the channel really isn't important here, consider The Hill's politics show on Youtube. No one would argue that The Hill's mission is to promote Sanders, but there is no doubt in the mind of anyone familiar with that show that it has a pro-Sanders bias in titles of its programs (and in the content of its shows, but that's not the topic here). People don't need to know an outlet's "mission" to detect bias correctly.