Without the CVR, we'll never know the truth sadly.
Equally, if the crew initiated the GA before ATC I wonder if it was PF or PM that called the GA. Remember they were studying the lights, and having doubts, for 2 minutes or more.
My thoughts and comments are basic on logic, and simple fact.
Do you really think the crew, after hearing UAL, seeing landing lights, and passing feet over aircraft, did not recognize it as the taxiway?
Did tower even say over the radio, you were lined up on the taxiway, and vector the GA?
Is it normal for aircraft to line up on the active runway for DEP? (facing backwards?)
IF what the NTSB stated is the case, that they stated they were lined up on 28R and did a GA because it didnt look right....
To answer other comments, they do the FMS bridge Visual, because all of the vector points and step downs are coded in, thus relieving ATC from all of that.
The CSPR procedures are a different lot.
A more constructive transmission would have been Air Canada you are lined up on the taxiway; or aircraft on approach to 28R you are landing on the taxiway.
How would UAL know its AC? One would assume that the drivers of all of those ac were busy with preflight, rather than stare out the windscreen plane spotting? In addition, if you are on Quiet Bridge visual, you approach the 28R TCH at an angle to extended centerline.