I saw this episode only yesterday, and was also intrigued by Heraklia's question: Why would Octavian go with Pullo on that nightly expedition to get Evander?

Some in this thread seem to agree with Skarr, that Octavian wanted to pay his debt to Vorenus by getting rid of Vorenus' "rival". But... would Octavian (Augustus) pay a debt without being sure that his creditor would be fully aware of it? Nah... not likely.

It seems to me that what Calpurnia suggested would be more in accordance with Octavian/Augustus: He probably helped Pullo in order to "win" him to his side and use him in a future time of need. That's totally "Augustan". Although Octavian was not Augustus at that time, the seeds were already there.