It doesn't specify anything on Foreign Earned Income, but I'm assuming it would fall under Zero Net Income Tax Liability, which if you've earned over $3,000 its saying for a single individual you're looking at $300 ($600 if filing jointly), under $3,000 you're looking at nothing.
In the text of the letter itself it states that anyone filing a 1040 (as long as its not a 1040NR, 1040NR-EZ, 1040-PR or 1040-SS) is eligible.

So, judging by that I'm assuming foreign earned income still qualifies for the stimulus.