Anyone know how the Iranians fuel their rockets? Hydrazine?
Possibly. Chinese space launchers have exhibited a distinctivly coloured smoke plume, similar to that of the hydrazine fuelled Titan ICBM. There appears to have been a fair amount of tech transfer from PRC to Iran - indirectly via Pakistan and/or NK.
Anyway, I guess they could have been 'mucking about' with hypergolic fuel, so no ignition source needed.
They might have chosen to do it indoors at an 'innocent' looking industrial site so sats couldn't get a look at what was going on.