I don't disagree with your criticism of his post, but to your question — as best I can tell, "founder mode" means maintaining a high level of personal involvement in product design and decision-making, even as the company grows. Trusting and delegating tasks to specific individuals but retaining a hands-on approach.

To some extent, the concept must remain vague because its meaning will vary from one company to another. Typically, there are one or two critical aspects that are most important for a startup or company, and the founder must be involved in those areas in a way that conflicts with the usual corporate structure or hierarchy.

Anyways, this is how I understood it.