Yes, it does seem vague. Isn't the NHTSA investigation meant to be a non-biased root-cause-analysis about last year's trailer crash? Instead, this just seems to be a grading report on Tesla's autopilot compliance.
There's no requirement that driver assist software magically become self-driving software in that situation. Put another way: it's nice if the software can avoid a problem, but not required.
The main remaining concern is that drivers not be confused about what they are required to do; there's discussion about that in this document.
This is probably why Musk pulled radar and vision processing in-house. Combining the data from both sensors is more effective, but more difficult, than combining the results from processing both sensors separately.