The map is really designed to be viewed from one angle, and I'm assuming the modeled out a bunch of individual assets, UV'd them, laid them out in the map, then used some sort of semi automated process to split the models into square chunks for streaming, used a tool to repack the UVs and make sure the texture resolution…
Thank you, everyone, for your inputs! The models were ripped from the game, I found the entire Summoner's Rift model and textures. So generally, the safest bet would be to treat the UVs using the best practices in the industry. I was just curious because it was very different from what I expected. And I guess it is best…