The round time from SFO to Mark Hopkins San Francisco hotel (where the couple was travelling) is at least 40 minutes and the cab driver was driving from SFO, not to it.
It's been 2 years, but here's the gist of it: cab drivers at the airport are allowed to jump back to the head of the queue if they are gone for a short period. Is it 30 minutes, or 40? Not sure. But I was told this personally by a cab driver, and also read it in the papers when this incident happened. Once the cab driver leaves the airport, he has N minutes (where in is a short number like 30) to come back. So cab drivers drive fast to get to their destination and then head back quickly. In this particular incident, it came out that the cab driver was aware of the mechanical problem but didn't stop to examine it because he didn't want to waste time.
The 30 minutes bit may be true but in this case, the cab driver would not be rushing as there would be no way the driver could return to the airport in time to beat the queue.
The article does not state that the driver was aware of any mechanical problem but only that "he had smelled smoke".