(1)Income other than capital gains Except as provided in subsection (h), there is hereby imposed for each taxable year a tax of 30 percent of the amount received from sources within the United States by a nonresident alien individual as—
(A)interest (other than original issue discount as defined in section 1273), dividends, rents, salaries, wages, premiums, annuities, compensations, remunerations, emoluments, and other fixed or determinable annual or periodical gains, profits, and income,
section 26CFR 871(h) deals with " interest of NRA received from certain portfolio debt investments" -- which have special treatment.
Thus my conclusion is a person whom is NRA and not living in the United States is subject to 30% tax on ordinary interest earned like savings bank etc. from US sources and no connected with United Sates Business.
Page 15 of Pub 519 ( which you quote) -- under the heading Non-Resident Alien ( implying while in the USA and being a Non-Resident Alien ) and then further on read pages 17 ---through page 21
Nonresident Aliens
A nonresident alien's income that is subject to
U.S. income tax must be divided into two categories.
1. Income that is effectively connected with a
trade or business in the United States, and
2. Income that is not effectively connected
with a trade or business in the United
States (discussed under The 30% Tax,
later).
The difference between these two categories
is that effectively connected income, after
allowable deductions, is taxed at graduated
rates. These are the same rates that apply to
U.S. citizens and residents. Income that is not
effectively connected is taxed at a flat 30% (or
lower treaty) rate.
A nonresident alien's income that is subject to
U.S. income tax must be divided into two categories.
1. Income that is effectively connected with a
trade or business in the United States, and
2. Income that is not effectively connected
with a trade or business in the United
States (discussed under The 30% Tax,
later).
The difference between these two categories
is that effectively connected income, after
allowable deductions, is taxed at graduated
rates. These are the same rates that apply to
U.S. citizens and residents. Income that is not
effectively connected is taxed at a flat 30% (or
lower treaty) rate.
All of these line come back to same that you , as an NRA and not residing in the USA and not in business , are subject to 30% tax on gross earnings ( with some restrictions). Perhaps , depending on amount of your earnings from US sources , you may want to consider filing a return on form 1040-NR ( mentioned above). A good source of help often is the nearest US consulate in your country--- they often have an IRS affiliate there and they are usually quite helpful.
Is there more I can do for you ?
pk
