Yes, Culture Is A Factor
Is it really a coincidence that majority Chinese Singapore has a bigger GDP than Malaysisa (only 24% Chinese) despite having a 5 times smaller population, while Indonesia (only 3.7% Chinese) whose population is more than 8 times bigger than Malaysia's only has a GDP that is less than 4 times bigger? Or is it really a coincidence that Israel is the only rich economy in the Middle East without significant amounts of oil in the ground, so rich that its GDP is larger than that of Egypt despite the fact that Egypt's population is 10 times bigger? Clearly some cultures, mainly Western and certain East Asian ones (Japanese, Korean, Chinese), are more succesfull in creating an advanced economy than others.
Chapman blames Israeli security based restrictions on the Palestinians for their poverty. But while that, and the conflict in general, is no doubt bad for the Palestinian economy (the conflict is also bad for the Israeli economy as they are boycotted by the Arab world and most other Muslim countries), that is only a small part of the explanation considering how Egypt and other non-oil producing Arab countries (who doesn't face these restrictions) are also far poorer than Israel.