so because the hijackers happened to speak Arabic prior to 9/11 then any time you hear people speaking Arabic (doubtful that it was even random) you are going to assume they're terrorists?!
No.
Hearing people speak Arabic is a normal thing. If that's their native language, cool.
Hearing two grown men yell Arabic across a plane when they aren't sitting next to each other . . . that would definitely have me shook. It's not politically correct to say but whatever.
I think it's moreso that the passengers don't know what they are saying and that they are yelling across a plane is what scares them.