The only person he could possibly help with this is Sanders, and there is no reason he would want to do that.
But still, this seems like a stupid thing for him to say.
Sure there is. If it could even slightly help Sanders get closer to the nomination, why not? Republicans believe Sanders would be easier to beat, which is why some of them were putting out ads that were intended to help him.
This little pseudo-endorsement has already riled up Bernie supporters like one would imagine. Of course, they are always waiting around for an excuse to insult / slander Hillary, so it's not unexpected.