Yet a government official can't block you on Facebook. Was that made explicit in the constitution?
I think the better reason is that they never actually told Meta to suppress the story, and I'm not sure if there was a stick to ensure that they'd do it.
A government official can block you. The office of government official cannot block you. As a general rule, objects in the Constitution (such as a press, personal things and affects etc) are understood to be defined by their function not by their form. Eg, 4th Amendment protection extends to your private correspondences via phone call despite no paper correspondence being present. Yes your hypothetical Facebook blocking situation is explicitly in the Constitution so long as you accept Facebook is a printing-press-by-way-of-function. If you refuse this minimal fair rule of interpretation, the Constitution is hopelessly stuck in the late 1700s.
I think the better reason is that they never actually told Meta to suppress the story, and I'm not sure if there was a stick to ensure that they'd do it.