Liability for water damage in rented condo (CA)

It seems pretty clear that an upstairs unit is liable for damage downstairs from a leak, but the chain of events causing it I can find no precedent of. Im renting a 2nd floor condo from a private owner. The toilet had developed some (non leaking, yet) issues and Im pretty handy so told the landlord Id fix it if he sprung for the parts. As thev often do the wall valve broke off in my hand so I had to turn off the water while replacing jt. There are two shutoff valves at the front of my unit, I ran water inside and felt the pipe to ensure I had the right valve. This valve is by the downstairs neighbors door, he wasnt home to consult or notify. While I had the pipe cut off upstairs, water began flying out of the wall. I raced downstairs to see the neighbor had arrived and opened the valve. He said "my water was shutoff" I told him what had happened he said thats impossible, this is my valve thats yours. I quickly realized that the one valve controlled the cold water for both units, the one he thought was for my unit actually controlled the inlet for the hot water heater we shared. He said I should have told him, I asked how could I if he wasnt home. I did ask him if it seemed prudent to just turn on a water supply valve if he didnt know why it was closed by someone. A few minutes later he informed me he had water damage to his bath ceiling. I havent seen it but only about 10 gallons were spilled and my floors are lightweight concrete. So not a lot got through, he claims there is a line from the vent to the wall. Today be informed me an inspector from his insurance agency was looking at it and wanted to know if it was clear or dirty water. (Clear) I informed my landlord, he isnt happy with me but said lets see what happens. I fear the neighbor will just tell his insurance the upstairs unit leaked into his and not mention his role in the incident. So the question is do his actions still leave me/my landlord with sole liability in this event? There is some damage to the hardwood floors in my unit but its not terrible. In a perfect world we would both own up to our roles in it and repair our own damage. However he didnt seem eager to admit him turning that valve was his goof. He didnt even know what that valve controlled, insisting it solely controlled his unit. In retrospect Id have tagged the valve but who just walks up and opens a main supply valve without investigating why it was closed? Again Ive disclosed the whole story to my landlord so if he gets contacted by his or their insurance, he knows the true story of the neighbors involvement.

Some thoughts about legal aspects: the plumbing was in a deteriorated state when I moved in. A tenant wouldnt be responsible for flooding damage, right? I was acting as the the tenant, not as a contractor getting paid who would have to have insurance. If it comes to whose actions ultimately caused the damage,wouldnt it be the neighbor's, for turning on the shutoff valve?

Any advice is appreciated.