No, he was not frauded. The DNC primaries are a completely different system that were manipulated not through election fraud, but the media publishing misleading polls to encourage voter disenfranchisement, unfair practices disallowing people to vote (a tactic the Republicans use in general elections, not Dems), and a coordinated effort to shift all voters from other candidates in the running to Biden with a mass dropout at the last second so Bernie's ground game couldn't respond to pick up those voters
I've been saying this for years