It's explained in the article:
"We expect $1,000 in additional monthly expenses (e.g. medical) 30 years into retirement (in today’s dollars, adjusted for inflation) and that amount rises to $2,000 after 40 years. This corresponds to the two spouses reaching a certain age where they may scale back other expenses (travel) but face increase medical, in-home care expenses, etc. that will case in a net increase in expenses."
"And, finally, the additional budget for medical expenses, care, nursing homes, etc., see below. This is now inputted as a negative cash flow!"
I have my own home-grown Excel spreadsheet. It accounts for my SS but, for various reasons, does not account for increased medical expenses in the future.