Whatever you eat gets dissolved by something like 10-20 teaspoons of stomach acid, which is roughly 100x-500x more acidic (linear scale) than honey. By the time it gets there a teaspoon of honey is not making a dent in the overall acidity.
I think it's mostly that somewhere along the line he missed how logarithmic scales work.
Hey, if it leads to your father consuming less unhealthy food (which milkshake and hamburger both arguably are) it works. Just for a different reason. And that different reason gives the faulty one credibility.
Unfortunately not, he just eats them at separate times!
Apples and oranges.
Unlike eating and excreting, the production (and destruction) of stomach acid doesn't change the body's overall pH.
Rather, the body produces acid by dumping alkalinity (specifically potassium bicarbonate) into the blood plasma.[0]
[0] https://teachmephysiology.com/gastrointestinal-system/stomac...
If those who ate too few acids found a way to induce the excretion of too many of them, then they'd be in trouble.
However, the mere fact that the body can remove something doesn't mean it's healthy, or that it doesn't stress the excretory system. See: ethanol, for example.