/jp/ - Otaku Culture

For Lumia, it sounds close to 'lumen' or 'lumiere' which means 'light' and that contradicts with her being a dusk youkai, which kinda adds to the idea that EoSD is supposed to be a deochi. For Rumia, it's mostly just people saying that it's a real European name which fine since EoSD is supposed to have a European feel to it because it's a deochi.

Personally, I don't think this is that big of a deal since Eastern and Little Nature Deity even translated her name as Lumia before it was later revised to Rumia.
https://web.archive.org/web/20100315044145/http://www.comptiq.com/release/comic/55touhou_owabi.html