There's an implicit assumption there, anything a computer as intelligent as a human does will be exactly what a human would do, only faster. Or more intelligent. If the process is part of the intelligent way of doing things, like the scientific method and careful experimentation, then that's what the ultraintelligent machine will do.

There's no implication that it's going to do it all magically in its head from first principles; it's become very clear in AI that embodiment and interaction with the real world is necessary. It might be practical for a world model at sufficient levels of compute to simulate engineering processes at a sufficient level of resolution that they can do all sorts of first principles simulated physical development and problem solving "in their head", but for the most part, real ultraintelligent development will happen with real world iterations, robots, and research labs doing physical things. They'll just be far more efficient and fast than us meatsacks.