You need to focus on the context of Rwanda before the genocide in 1994, and the deep tribal divisions that had dogged the country for so many generations beforehand. All this produced a simmering resentment that was barely concealed beneath the surface of the country and resulted in the Rwandan genocide. Clearly tribal migration also was a key component in this sad story, as first Tutsis then Hutus fled the country.
Rwanda had been a very unstable country for quite some time when the genocide of 1994 occurred. There had been a civil war, various rebel groups fighting for power and refugee populations shifting away from the fighting. When the genocide occurred, many of the same push/pull factors were involved, but they happened in a faster way.
The major push factors had to do with refugees fleeing the murder that was taking place once it started, Tutsis who were trying to make it to Tutsi-controlled areas so they would be safe, or leaving the country altogether. Violence on this scale is a very powerful push factor. It happened again at the end of the genocide when the Tutsi recaptured the government and the capital, and 2 million Hutus fled to Congo in fear for their lives.
The major "pull" factor was the pull of home, and the desire to return there to family and to what's familiar once the violence had stopped. It's difficult to live on the run or in a refugee camp, and this pull factor brought most of the refugees of both peoples home eventually.
The definition of a push-pull factor is "a force which acts to drive people away from a place and the pull factor is what draws them to a new location." The genocide itself forces people to evacuate ares in which they had lived and forces them to other places or other countries. Then, when the fighting subsides, people feel the need to return to their homeland.