Clearly Bernie is no saint and there are many issues I have with him. However, he did move the Overton Window on Palestine, and many other things. I don‘t see how he could have taken the conversation further in the context of an election where he is trying to get Jewish votes.
I’ve read some of those conspiracy theories. In my mind the more plausible scenario is; Clinton threatened to ruin the career and any pet projects of any Democrat who challenged her if they lost. She knew it would be ridiculous if no one else sought the nomination so that threat was lifted for a select few people who Clinton deemed uncompetitive.
I am sure the Clinton campaign saw it as a way to lure back in the left once he started getting traction. Sanders does not strike me as the type to willfully lie to your face, much less be part of a months long subterfuge to hoist up someone who he does not like.