I would expect a growth mindset as applied to health and fitness would recognise short term versus long term benefits. Maintaining a healthy bodyweight decreases the risk of all cause mortality. Losing weight to the point of anorexia would cause numerous potential problems, and quickly be recognised as not ideal and a different approach applied.
Optimising conversations only for maximum knowledge extraction is not a valid approach within the broader goal of optimising social interactions to maintain a healthy group of friends and family who you enjoy spending time with and can depend upon for years to come.
A diet of pure protein shakes and broccoli is clearly not in line with any reasonable approach to a healthy diet which instead should aim to have a broad a varied source of nutrients, again with the goal of maintaining long term health and supporting whatever sports/training/activities the person takes part in.
A programmer/software engineer who is serious about improving their craft would be much better served by taking a holistic view of their role and expanding their knowledge and expertise to a much broader set of skills than just algorithms and data structures.
Your hypothetical deranged person I would argue is operating under the exact opposite of a growth mindset.
I'm lambasting the "growth strategy" that leads companies to release worse products via over-optimisation. I am pointing out how this sort of 'growth strategy' would lead to absurd behaviours if a human applied the same logic.
I think it would be reasonable to class his mode of being as that of individual growth mindset.
Analogy is a literary device for conveying an idea. You obviously understood the idea being conveyed, thus, the analogy did exactly what it was meant to do.
The point isn't that the particular strategy for health and fitness is right or wrong, it's that the growth mindset causes the person (Bob?) to over-focus on that aspect of their life to the detriment of more important but less obvious ones, like personal relationships, being kind to others, or enjoying fallen leaves in autumn.
Bob spends his 20s trying to improve his bodyfat percentage, max his bench, get a Porsche, and build his 401k.
He misses out on his niece's early childhood, loses his highschool friendships, and breaks up with his girlfriend for a job opportunity in a different city.
This is like the printer company focusing on revenue instead of brand loyalty or its reputation.