Maybe I read the article incorrectly, but it specifically states that income derived from foreign businesses is tax-free. So this should include any freelance work or employment with a foreign entity as well as business profits derived abroad. I don't think the "butt in seat" rule applies here.
It is a good idea to bring this up in any case, because there could be other tax implications, especially for Americans unaware that they will be paying tax on income above $108,700.
It doesn't matter where the employer/client is located. Income is taxed _where the work is performed_. If you work in Indonesia that's where your income will be taxed.
"Business profits" are different, since they are generally regarded as dividends distributed to shareholders who (in theory) don't "do work" for the company.
It is a good idea to bring this up in any case, because there could be other tax implications, especially for Americans unaware that they will be paying tax on income above $108,700.