That's one way of interpreting it. But if you read all 14 pages at no point does the "guideline" identify anything that classifies a weapon as an SBR - merely that it depends on caliber (not specifying which ones), use of a close eye relief optic (not specifying types, kinds, brands, models, etc.), whether it is oriented properly for one handed shooting or points up or down (really?), etc. etc. It is at their sole discretion if a braced pistol is a braced pistol or an SBR with no information at all providing a guideline. It would never stand up in court (probably even a liberal one).
Another way of reading it is exactly as it says...the ATF doesn't have the ability to create law (they don't). They DO have the ability to create a scare and in so doing potentially stop manufacturing of braced pistols, increase registration, and greatly inhibit their sale and possession. The document even states that enforcement of it is at their whim (not their exact words - but their essential meaning).
I was actually planning to SBR (submit the paperwork, not add a stock and vertical grip - yet) my DD MK18 over the holidays anyways. If they can make it to where I can do so in an expedited manner and not pay the $200 tax - I will but not because they say I have to, only because I planned to anyways.
I'll be the first to admit I'm not a lawyer, but I believe that paragraph indicates that the document you read is a guide on what they intend to publish to the federal register. It does not become law until that point, after that point it is. It speaks of a process by which owners of current stabilizing brace equipped pistols will be required to register under the NFA or remove and destroy their stabilizing brace.