Nah it's not just pure coincidence that a 4/5 vcs and founders have similar economic backgrounds.
Ev came from an unusually humble background for Silicon Valley.
Steve Jobs was from Silicon Valley but grew up poor.
Reid Hoffman's mom hooked him up with vc money and a network, cause she was a rich lawyer at a fancy firm iirc.
Very few people that grew up poor are successful in Silicon Valley but they may be the most impactful as a population.