I made digital products while in a foreign country. These products were sold through a marketplace in the US. Is this work that took place within the United States?

[Carl]

Making/manufacturing a product and selling a product are two physically separate things. You must be physically present in the U.S in order to make/manufacture something in the U.S. However, you do not have to be present in the U.S. to sell something in the U.S.

[Opus 17]

If you are a US citizen or US resident alien (green card holder) you are required to report and pay income tax on all your worldwide income, regardless of where you lived and worked at the time.

If you are a non-resident alien, you only pay US income tax on US-source income.  If you live and work overseas, the fact that some of your customers are in the US does not make that income US-source.