It's a sensational story, which on the basis of that very reaction leads me to think it's just that. The US simply wouldn't let the Saudis have nukes as it would destabilise the region and only fuel the Arab arms race they're so keen to avoid. Or, put another way, the US may be underwriting the Saudis militarily in the event of Iran etc getting boisterous, but that will be conditional on them shelving their nuclear ambitions.