That helps to explain a reason. Must say, it's a long time since I operated into SFO and don't recollect the offset.
There is an offset LDA and LDA (PRM) approach to RW28R. FAC 281. (RWY QFU 284.)
There is also a regular straight-in ILS approach to RW28R with FAC 284.
My understanding is that the Air Canada was cleared for the "Quiet Bridge" visual approach to RW28R. This involves an initial course of 275 towards the SFO VOR (centre-field) and then an alignment at 6D (5nm from THR) to the RWY QFU of 284. The 28R ILS GS is available for vertical guidance.