I have read this before and believe that Jesus has indeed returned already. This theory is interesting and is the only other option aside from Jesus truly being God and the validity of Christianity proven fact. I don't know what to think of it though - there isn't any historical proof for it. But the coincidences and interpretation should be looked at closer.
The preterist view of scripture is that the siege of Jerusalem was the fulfillment of Jesus's predictions and Revelations. God always used foreign nations to bring judgment upon the Jews - that Titus was leading the siege is no surprise.