Um, yes he would, or should, have been masked. Even incidental collection on an American citizen is not permitted. No matter what agency does it.
As soon as you realize one part to the conversation is American the collection stops. Period. End of story.
You want to get more then get a warrant.
You can dig it out of here
https://www.dni.gov/files/documents/1118/CLEANEDFinal%20USSID%20SP0018.pdf
If you place a call on your mobile phone while youre in a foreign country especially a third world sh!t-hole like the Dominican Republic there are probably dozens of shady characters who have access to your conversation before the CIA/FBI does.