The article is saying housing in San Francisco is unaffordable compared to San Francisco's own median income. I'm not an economist (nor a San Franciscan,) but that sounds unsustainable no matter how you spin it.

This can occur when an influx of high paying jobs raises prices but the original, poorer inhabitants are unwilling to move out. Eventually the median income rises as people retire, die or can no longer afford the property tax on their now-very-pricey homes. The few remaining low income jobs are staffed by commuters.