While you are correct that the epicenter was too close to San Francisco for a 20 s P-S delay (by far, as you suggest), the article said "the bay area", and there could have been a pretty significant delay in place like San Jose (if it existed yet...). As far as the quake occuring 100 miles from San Francisco-it did occur well over 100 miles from San Francisco. It also occurred a few miles from San Francisco. Its epicenter is considered to be near the Golden Gate, so that is the distance that would be used for the first P-waves. It ruptured well over two hundred km of fault -according to the California state fault map (Jennings, 1994). For a M9.2, like Alaska 1964, it ruptured not only 600 km along strike, but a much larger area downdip (because it was a shallow fault, the area is much larger than a sub-vertical fault), and the slip was much more. Chile 1960 was M9.5 and ruptured 1000 km along strike. I've heard that the slip was as much as 100 m, although that seems hard to believe. The slip in the San Francisco earthquake was as much as 4 or 6 m.....
Chris