Why are you so upset about this? Let's assume, worst case scenario, you're totally right and Bernie Sanders pused a conspiracy theory involving Jeff Bezos, mega billionaire and exploiter of workers, having influence at WaPo, the most influential newspaper in America. Despite Sanders clarifying what he meant, let's go with that assumption.
What's the consequence of this?
It builds distrust in corporately owned media and increases class consciousness
Fucking tragedy if you ask me.
BUT THE REAL PROBLEM IS HE DID A FIB ABOUT IT
To me, it seems you're more concerned with Sanders making an unfounded accusation, which he clarified, or in your words, "changed his mind on", than the extremely real problem of our media being completely biased against DC outsiders and people advocating for the lower classes in a serious way.
Which is... an extremely trash take.