They were both heavily backed by DSA individuals, their ground teams composed of DSA volunteers using DSA resources. Sanders was officially endorsed. A system is what is produces.
You can’t use the “they aren’t officially members of DSA” defense while the DSA endorses and backs and gives resources to electeds outside of the DSA constantly as a matter of process. Why don’t they stick to backing official DSA members only instead? Then that would be a valid defense.