I watched this livestream on Twitter/X, but missed the beginning. At the end, there was a prominent, unambiguous banner saying that this event was filmed and on the record, or some words to that effect. It seems likely that all were aware that this event was going to be public.

I was listening in the background and seem to remember hearing something like what you quoted, but not sure if they were referring to an earlier event or if he said it on this stream.

https://x.com/chathamhouse/status/1920447338692145584