It was not hard to be vegan in Rwanda. Not at all. What was difficult was finding a large variety of vegan foods. Because of the leisurely pace of Rwandan restaurant service, we almost always ate at buffets. At every buffet there was always rice, potatoes (several kinds - roasted, boiled), sweet potatoes, and always boiled greens such as spinach or cassava leaves (surprisingly tasty), as well as a bean stew of some kind - beans with green beans, or beans with sweet potatoes, or beans with beans. We were never worried about being short of protein, just short of variety.
We were glad that we brought a jar of peanut butter with us, because breakfast most days was toast and fruit. There were eggs on offer but of course, we don't eat eggs.
Animals being taken to slaughter are treated poorly in North America. From what we have seen, they are treated worse in Rwanda. Four years ago, I saw cows stacked (yes, stacked) in a truck as we drove along a highway. Last week we passed a truck with pigs tied to the top of it.
We could not have been the only vegetarians in Rwanda, yet Rwandan waiters and restaurant staff looked askance at us if we said we didn't want cheese with our brekkie or milk in our tea.