No, everyone was not poor back then, at least not in the roman empire. That's what the Gracchaian reforms were all about. That's by the brothers Gracchus were murdered. Some people, for example Cicero, were quite rich, while most people were extremely poor. Because of roman city planning, people were keenly aware of the disparity. It was a continual source of strife in the late republic and early empire.
About transcending tribal differences, this is actually how the Roman religion worked. New gods could be and were added to the pantheon all the time. This obviously couldn't happen with Christianity. Rather than building and spreading civilization, Christianity was spread by a civilization and led to quite a bit of conflict along the way. Funny enough, the only religion the romans ever really tried to kill became the world's most wide spread religion.
I imagine that he would be referring to the areas where the "fable" of Jesus Christ started spreading from, at the hands of men like St. Paul. I think it would be fair to say that these areas were probably dirt poor at that time, and quite far off their days of glory. The Jewish civilization was on the decline, and under Roman control.
So it was probably not the Semites, originally, that invented Jesus as a social control mechanism against the poor. If anything spreading Jesus's word may have been more of a "last hope" to empower the poor people in these areas. Indeed, it appears that Christianity, initially, was mostly a religious cult for social outcasts. Fanatical, beyond doubt, but not overtly powerful or influential.
But it is fully possible that the Romans, at a later date, saw the possible advantages in having the poor people of Rome believe in a benevolent deity and an after-life, instead focusing on secular matters, such as the increased division between the classes that partially led to Rome's decline. Rather than treating Christianity as a threatening social movement of the poor, as they had originally done, they decided to absorb it and mold it to serve the state's best interests. And thus, the corruption of the church and the "spirit" began, from the very day the organized church was established.
Of course, there's so much that we don't know, and never will know, about the origin of Christianity, that everything of this sort is basically reduced to "educated guesses" and speculation, even on the part of expert historians.
Making a statement such as "the story of Jesus Christ being fabricated to pacify the poor", sounds bold and bombastic, and possibly even logical, but in reality it's the statement of a hack. There's absolutely no way of verifying that statement on facts. It has been two thousand years since then, and unfortunately, not all of the records were well kept, including the potential original source material that may have been used as reference to write the gospels.
It would be more appropriate to say that the story of Jesus Christ has indeed been used to pacify the poor, many many times. That would be 100% factually correct.