From what I've heard, Hutus were targeted for being moderate, like Acting Prime Minister Madame Agathe Uwilingiyimana and human rights worker Monique Mujawamariya.

The practice of killing some Hutus in order to convince others (mostly reticent local leaders) to join the genocidaires and mobilize their people was also institutionalized.

There was also believed to have been widespread false registration (believed to be Tutsi claiming to be Hutu - this is cited as the major factor in the difficulty in numbering the murdered).

The genocide itself was extremely well organized, with orders going down an institutionalized chain of command, and reports coming back up that same chain.

Fears among the Hutu (shamelessly exploited) were exacerbated by the assasination (by Tutsi) of the freely elected Hutu president of Burundi.

Members of the Rwandan akuza ("little house" - the group of business and government elites centered, not around the president Habyarimana, but his wife, it was also called the "clan de Madame") were seen in conversation, sharing beers, with army leaders directing the genocide in the early hours and days after the president's plane was shot down and the killing began. They are believed to be central players, one of whom actually imported the thousands of machetes to be used by the Interahamwe.

All this tends to argue for political rather than Mathusian causes.

There is evidence for your claim, though:

"At the end of the 1980s, coffee, which accounted for 75 percent of Rwanda's foreign exchange, dropped sharply in price on the international market. Suddenly Rwanda found itself among the many debtor nations required to accept strict fiscal measures imposed by the World Bank and the donor nations. The urban elite saw its comfort threatened, but the rural poor suffered even more. A drought beginning in 1989 reduced harvests in the south and left substantial numbers of people short of food. Habyarimana at first refused to acknowledge the gravity of the food shortage, an attitude that exemplified the readiness of the urban elite to ignore suffering out on the hills." (emphasis mine)

--Leave None to Tell The Story (pdf, 540 pages), Human Rights Watch report on the Rwandan Genocide, Alison Des Forges et al.

Famine happens all too frequently, and is not always accompanied by genocide (Somalia, for instance). All else being equal, would the Rwandan genocide have happened if the country was prosperous, well nourished and without the large unemployed population? We'll never know, but I doubt it. Lots of things went into the events in Rwanda in 1994 that were driven by those parts of society which were living very fat indeed.

"It Can't Be Just About Us"
--Frank Schnittger, ETian Extraordinaire