Doesn't matter why a surface is lit (self-lit or from a light) the secondary lighting sampled by other surfaces picks it up. When the light source is 100% indirect, as in my entire room, or in your room with any props in 100% shadow, then the artifacts are more obvious. If secondary light is only a small fraction of a given surface illumination, then the artifacts are less obvious. Signal to noise ratio is being altered, where the noise is constant, and the signal varies. When the signal is strong (direct illumination) the noise is a smaller fraction and harder to notice.

Your Wibbly looks pretty good to me. One render is certainly no proof, but I didn't run into any problems. This is in your room. 28 seconds on my craptop.

Standard dialog settings, not D3D:

Bounces = 6
IC = 30
ILQ = 0!!!
Pixel Samples = 4
Min shading rate = 1

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)