If a sprinkler system can't put out a fire started by one guy with a lighter and some boxes (no chemical soaked rags, no gasoline, etc.), that building cannot be occupied.
Bank on it that the sprinkler system was to code for light industrial use but not for storing that volume of combustibles. Also bank on it that there were no internal walls with closing doors to stop the spread as you would do with combustibles.
I spent a lot of time going through sprinkler system installations for aircraft hangars and multi-use facilities. We even had hangars with two separate systems installed - one for aircraft and another for deployable assets. Someone has to spec the contents, determine the burn rate, determine the water pressure, and of course cut the check.
No one wants to cut the check.
As a retired fire inspector, I can say you are spot on. What most people know about the intricacies of modern building fire protection they learned from Hollywood movies.