>Paul Kagame's anti-corruption policies are impressive

Indeed, you will find very few that would argue with that. Also, there are clear economic and social benefits to little/no corruption. However, Rwanda's good fortune in fighting corruption in a sea of systemically corrupt countries (the neighboring DRC and Burundi are notoriously corrupt, but that still pales in comparison to Kenya, a country that hosts numerous Rwandan nationals) stems almost purely from the political will of one man- Paul Kagame. Without the political authority and moral mandate that he wields, these anti-corruption policies would be no more effective than they are in countries across East Africa (Somalia, South Sudan, Burundi, DRC, Uganda, and Kenya are among SSA's most corrupt countries, and all are within 3-hour flights from Kigali; this shared geography also means that East African countries have shared political, social, and economic fortunes/identity. For instance, numerous Rwandan citizens see Kenya/Uganda as a second home. For example, my childhood pastor was Rwandan and so were many of those that I went to primary school with. I say this to emphasize the fact that Rwanda is not uniquely tooled to fight corruption, just uniquely ruled).

>find a proper black middle class

I doubt Rwanda is the only EA country with a proper middle class. I also doubt that any such middle case would (entirely) owe its very existence to anti-corruption policies. A far, far larger percentage of Kenyans fall within the ADB's classification of middle income than their Rwandan counterparts. Kenya is a significant (if not the most significant) source of foreign direct investment to Rwanda. In addition, Kenya also has the highest per capita car ownership anywhere in this part of the world. I am really not trashing Rwanda, just saying that when put in perspective, the country still has a long way to go.

You did not mention the genocide or the country's attempts to recover from it. Perhaps there is something to be said of the matter. Over 100,000 people lost their lives in 100 days at the hands of neighbors, students/teachers, relatives, etc. The shock of the genocide is something that,as a Kenyan, I can relate to. Not too long ago (2008-09), over 1,000 people lost their lives to post-election violence. In the aftermath, a coalition government was formed, a new and superlatively progressive constitution promulgated, land reform enacted, and former adversaries became formidable political partners. A lot has yet to change, but the impact of those clashes can still be felt to this day. Rwanda rebounded by centralizing power in an evidently aggressive and autocratic political leadership: 'contrarians' were exiled and speech constrained/censored. For instance, it is anathema to explore the role that Kagame's Rwanda Patriotic Front played in the '94 genocide. The revisionism of the present government has become an important concern, but only for those outside the country's borders (or reach). This response is somewhat comparable to China's efforts at enforcing a sanctioned narrative around the Tiananmen protests and killings and is not a sustainable path to enduring peace. Surprisingly, this is something that I am seeing more of in Kenya, where two of the chief adversaries in the post-election violence are now political incumbents.
That said, Rwanda has made an impressive social and economic recovery from the unimaginable tragedy that it suffered two decades ago. Regardless, it is far from becoming the sought of tech hub that CNN and others would like us to believe.