After looking online, everything I've found says the breakdown of ethnicities was 1% Twa, 85% Hutu and 14% Tutsi immediately before the genocide as well as in present day, and I haven't found anything about the period right after the genocide. It seems to me that the surviving Tutsi population would have to have bred prodigiously to get the Tutsi population back up to a level where it made up 14% of the population after 3/4 of them were killed.
well there was and is a lot of movement of various tribes across national borders, especially between rwanda and congo, as these borders often intersect traditional tribal territories, so that may help explain at least some of the discrepancies. There are regular news reports on issues around the border of these 2 countries today, heres a recent one: http://www.ndtv.com/article/world/african-rivalries-weaken-un-hand-against-rebels-in-congo-610470 Also, many may have fled and returned. additionally, its questionable how accurate data sources reporting on ethnic breakdowns in rural areas are, especially before the genocide; its very hard to get reliable estimates of this info. For more info theres a BBC documentary called Rwanda: The Untold Story.
The genocide was ended by an invasion, an invasion that largely ended a tutsi diaspora and was accompanied by the return of hundreds of thousands of Tutsis to the country.