Assuming ~90k of household income before taxes what he describes is definitely possible in the Boston area (which I know is not the most overpriced city but it's definitely on the leader board). You just can't be too good to live in an apartment where you see occasional mice and go out to eat at the Chinese buffet of questionable quality and drink mass produced domestic light beer. Basically you have to live below your means, not the way someone who's making STEM money is expected to live.
Two recent grads making a combined 90k pre-tax is 45th percentile for a household for Boston (per the calculator you linked). You have to actually prioritize it and consequently make all your little day to day decisions with an eye towards cost (which is going to be very hard for an upper middle class person who's never done that in their life to suddenly start doing) but you can definitely aggressively pay down debt or save money.
