From a rational standpoint, I don't understand how investors could feel betrayed by a pivot that involves creating two ovens to eventually allow the founder to capture 10% of the market. Functionally, I can't imagine a single investor actually caring about these details. They don't care about the number of buttons, or if it can do wedding cakes, or whatever. They care that the founder and team demonstrates competence in their decision making and execution.

If a founder is able to spin and control both the loss of a major potential customer, and the low customer satisfaction rate (weak follow up from pilots) to the investors, I simply cannot imagine that doing 2 product lines is that much of a big deal.

More personally, I'd feel that if it truly were a coldly rational decision, the founder would feel confident in defending his choices (at least against any initial suggestions to the contrary) without resorting to anger.