Whether or not this is the case, I don't get this as being the reason for Sousmith leaving - it sounds as if he is just ready for a change.
Still, it is noticeable that with many of the AI companies claiming that their version of "AGI" is just around the corner, developers and staff don't appear to be particularly excited about this (I assume they realize it is just hype, not some momentous advance around the corner), and leave to pursue different things, such as Mira Murati starting a fine-tuning company, Karpathy going back to education, others switching ship (typically from OpenAI to Anthropic), etc.