| Falcon 9 rockets burn RP-1, a hydrocarbon fuel, so the oxygen is being converted to CO2, and CO as well as H2O. [1] Beyond that, I don't think the direct comparison of mass is definitive. Much of the rocket's fuel is expended at lower altitudes, and much of a volcano's ejecta return quickly to earth as ash or rain. It would be important to understand what percentage of a volcano's ejecta reaches the height of these clouds as well as what percentage of a rocket's exhaust is produced at that height. Just to throw in some round figures: noctilucent clouds are formed between 80 and 85 km altitude [2] large volcanic eruption plumes top out somewhere between 31 and 45 km [3] Falcon 9 launches stage at 80 km [4], meaning 23% of their propellant mass [5] is converted to exhaust at that altitude or higher. So while I'm no expert on noctilucent cloud formation and happy to be given more info, the prima facia case seems to favor rocket launches seeding noctilucent clouds much more readily than volcanic eruptions. [1] https://en.wikipedia.org/wiki/RP-1#Comparison_with_other_fue...
[2] https://www.albany.edu/faculty/rgk/atm101/nlc.htm , though other sources give a wider range of 76-85 km.
[3] https://volcano.oregonstate.edu/faq/how-high-can-explosive-e...
[4] https://www.nasa.gov/wp-content/uploads/2018/07/spacex_nasa_...
[5] https://en.wikipedia.org/wiki/Falcon_9#Design |