As stated in Timatic, the database used by check-in staff at airports (to determine whether to let you board the flight):
Visa required, except for holders of confirmed onward air
tickets in transit through Guangzhou (CAN) to a third country,
for a max. transit time of 24 hours.
Transit incl. multiple stops within China (People's Rep.)
is permitted at Guangzhou (CAN) only when the first transit
point is Beijing (PEK). The total maximum transit time is
Depending on the country, even a technical stop not involving clearing immigration may count as transit, and Timatic doesn't indicate this not being the case.
The determining question here is: does the technical stop at Wuhan count as a transit point? Timatic doesn't clarify this, unfortunately.
What you need to do is call the airport, ask to speak with a supervisor of the ground handling agent responsible for China Southern and ask this specific question (the flight number is CZ 660).
If the technical stop in Wuhan does count as a transit point, you will need a transit visa: because multiple-stop visa-free transit at Guangzhou is only allowed if the first transit point is Beijing.
If the technical stop in Wuhan does not count as a transit point (in which case get it in writing from the supervisor), you do not need a visa
Once again, it is the ground handling agent responsible for China Southern at SFO that you have to contact, because their interpretation of the info in Timatic is the thing that determines whether you'll get on the flight.