to answer your question, he's been a core contributor to many core primitives and novel techniques in three.js, r3f, drei, postprocessing, etc. so, very likely most people vibecoding with three.js are using his work. not to mention projects like four and ogl outside of the three ecosystem.
you're right this is fully permissible under the licenses though that's not really the salient point he's making, which was that there's no attribution or provenance for any sort of creators with LLM's, which discourages future contributions from the giants shoulders on which these ecosystems stand. this is a structural incentive problem which may cause the ceiling to be lowered over time for open projects due to a shrinking pool of contributions. practically speaking the fear for three.js would be that it loses some of its best contributors like Cody, which would of course be net-bad for anyone vibecoding with three.js as it regresses to the mean
in any case I enjoy following both of you and I'm not sure what bone is being picked here