Just checking, CELT & Opus are the same thing? Seems like they're saying that Opus is a merge of CELT & SILK

Yes, Opus is basically a merge of CELT and SILK.

SILK is a speech codec developed by Skype whereas CELT is a general purpose audio codec developed by Xiph.org. Opus can use either of them (to encode speech or e.g. music, respectively) or it can use both codecs simultaneously for high-quality speech.

And Holy Fxxk that is some awesome Hardcore Video and Audio hacker discussion. Great Stuff!!!!