If a village center generates close enough to the edge of a biome, then parts of the village will quite often bleed over to that biome. Examples include a desert village that is partly in a plains biome, a plains village party in a desert biome, or many other examples. Just to be clear, the village center spawns in the correct biome, it is just that the other buildings in the village will often spawn in the wrong biome.

Reproduction is quite easy, as this is a very common bug. You simply need to spawn in a world and keep looking for villages until you see one that has spread into a different biome, which should not take terribly long. The picture below is seed -8942429258204498561, and the coords are 893, 98, -259, on 20w19a.