Non-salary fellowships and US income taxes
Fellowship funds used for personal expenses including room and board, food, etc, are taxable, just like it says in the passage you quoted.

If social security taxes, medicare, etc, is not withheld, you don't need to pay those, since it is taxable income but not taxable wages. In that way, a fellowship is treated like any other academic scholarship that includes money for living expenses, rather than like an hourly/salaried position.

See also How much are taxes for a postdoc in the United States? though that question is not specific for fellowship-based income.

Fellowships awarded to individuals that include other expenses, like research expenses, are typically granted to the institution not to the individual, so those other expenses would not be part of your personal income even if it is an individual expenses. If they were paid to an individual, you would likely be able to deduct them as business expenses, but you would be best off working with an attorney or tax professional in that unusual situation.

If you are talking about receiving a foreign $50k fellowship in addition to a foreign $50k salary abroad, then yes indeed you are approaching limits for exclusion of foreign income but it is unlikely you will be taxed twice on the same income due to foreign tax credits for US taxes, but that is really now an issue of tax law for expats and not really related to academia specifically; that situation seems like it would be quite unusual in academia for a post doc, and although it may place a burden on a researcher, an income of $100k+ would place you in a fairly high percentile of individuals where the US government expects that there is a burden on your income to pay for the costs of society - this is true in many other countries as well.