That's what I originally thought as well when I first played the game, because as I said, it makes no sense to get both the Vault 13 population as well as the Arroyo people unless that was your goal. Make sure it works on one but not the other. However, there's these tidbits:
As Risewild said, President Dick says that any humanoid that
isn't inoculated against it will die. So, basically you need a vaccine against it in order to be spared from the effects The Project, being death.
There's also this which you can download from a terminal in the oil rig:
Final tests conducted on the vault-descendant subjects, from the village "Arroyo," have shown a survival rate of zero-percent, with most deaths occurring within one-hour of exposure to a .0001% aerosol solution. By contrast, the subjects extracted from Vault 13 tend to suffer subdural hemorrhaging and convulsions within one-hour of exposure, with death not occurring, on average, for another 14.5-hours.
So, it still kills the Vault 13 people, but it takes more time. And this was the "successful" test. It just seems to me that they started with what you thought, and what I originally thought my first time playing it, and then changed it late in development to where it killed everyone that didn't have the inoculation.
It could be poorly worded, and they mean that after 14.5 hours, the symptoms go away. But then why make an inoculation if the goal is to wipe out just "mutants" and leave the vault dwellers and other non-exposed people alive if the goal is "pure humans"? Also, you can kill everyone on the Oil Rig that isn't inoculated with the FEV Curling-13 by releasing it in to the air system. So it does work on them unless they're inoculated.