So, I rechecked this scene too (it was the one just before, so I'm glad not to have searched for hours):
The "infinitesimal" thing we're talking about? It's stated nowhere.
Yog-Sothoth is the "New World/Other World" (in context, it mean Multiverse btw), which was summoned by Master Therion. What Yog did was trying to "overwrite" the current Multiverse with himself, while also opening the Gate between the 2 Multiverse.
For Chaos, see what I said before. And non-existence was just mentionned one time without any precision.
So while the statements we currently had indicated something like Low 1-C or possibly Low 1-C, there's in truth nothing which would confirm anything beyond 2-A/At least 2-A.