There's been a list for a couple of decades now, used to stop "Muslim terrorists" that has been repeatedly used to harass individuals with no ties to terrorism. It has repeatedly proven really easy to get onto that list, and really hard to get off it.

It is more likely that his flight has been cancelled considering ongoing government shutdown.

it seems like a failure of journalism that the guardian didn't try and reach out to the airline to find out why this guy's flight was cancelled. if the guardian did do this and didn't find an adequate explanation then they should say this in the article. this just seems to be this zero-value-add reporting where reporters are served up information but then don't do any extra work to find out what the fuck is actually going on. its totally possible this guy is being persecuted by the TSA. there was the quiet skys program which i think is for domestic flights and is meant to have been abandoned but presumably there is something else for international flights where the TSA or homeland security can persecute people they don't like.