To be fair, Lamont has been consistent in his whole campaign in not accepting any PAC money from anyone (except from "leadership pacs" i.e., the treasure chests of elected officials). He's rich enough to finance himself, and this was his chosen way to transmute "being rich" into "being clean." When SEIU offered him 5000 bucks at a public rally he refused that too, and then they offered him volunteers instead, which are a much more valuable resource from his perspective.
So I don't think there's any evidence at least on the surface for interpreting this gesture as hypervigilant fear of a socialist taint.
Michael