It's not all that speculative - it agrees what was in prior leaks that claim that American companies are routinely infiltrated. Also remember that the authors of these articles have read huge volumes of Snowden documents have have not been publicly released and that the security experts (likely referencing Schneier here) are not just guys working in private industry. If you work in the security space you very quickly begin to interoperate with past- and current- military and government personnel. Schneier testifies as an expert witness on these things before congress and Greenwald is an ex-Constitutional lawyer. In short they have the pedigree to make these assertions.

For the record I don't agree with the parent. I think the important thing about this document is that it lays out the broad tactical tools used in US cyberintelligence strategy. It's handing off some major tactical playbook material.