He details around the 1:10 minute mark about how he was sidelined (which I incorrectly interpreted to mean he had been forced to resign) for suggesting that both lab leak and natural origin theories should be investigated. Apparently he was simply left out of the discussion entirely after sharing his position, and resigned later, but I haven't actually been able to find any details or the exact reasoning behind his exit from the CDC.
That being said, him being sidelined is, in my opinion, still extremely concerning. It's pretty clear to me that him disagreeing with Fauci lead to him being pushed out, but there doesn't seem to be any info anywhere on the subject.