If the recipients could only afford a traditional mud + thatch home, the contractors building work was new additional demand, rather than competition against existing builders.

Even when first-world funding dries up, knowledge of the design, its features and benefits will remain. It's also cheaper than the alternative single-storey concrete home design, so perhaps generating new construction demand from people who couldn't quite afford the more expensive single-storey stone house but can afford this new design.

It's certainly an eye-opening unusual project, but I think it's a net gain for the region, even without a sustained/permanent first-world benefactor.

You would almost certainly have got a bigger next gain for the same cost if you gave the same people the money used to build the house.