TT is claiming I am eligible for the Foreign Tax Credit when I correctly entered all W2s. All income was in the US. Would stock investments trigger this?

Yes, dividends paid from a foreign stock could trigger this if your Form 1099-DIV shows a foreign tax paid in box 7.  There may be other triggers as well, but foreign dividends is a common one.  

The following TurboTax help article will provide more information about how to claim the foreign tax credit:

Where do I enter the foreign tax credit (Form 1116) or deduction?