I was curious, so I researched it (aka prompted ChatGPT). SFO-PVG was established in 2000, long before Apple offshored all of their manufacturing to China. An article from the time describes it being something that was in demand among Silicon Valley in general[1] rather than Apple particularly. In 2019, United revealed that Apple does spend $35 million/yr on that single route, averaging 50 seats/day[2], so I suppose that's the source of the legend.

[1]https://www.sfgate.com/business/article/shanghai-to-s-f-flig...

[2]https://www.macrumors.com/2019/01/11/apple-united-airline-pu...