There is something strange about this temple. Emperor Vespasianus died in the same year as the eruption and he is known to have said when he died:" I believe I am becoming a god". This indicates he did not present himself as a god during his time as emperor ( as Caligula had done). So it's unlikely this was a temple in the honour of his genius, since he died in 79, the very same year of the eruption. Probably this was a temple for Augustus