Uh, so how did anyone even know the guy was praying? Was he bowing face down in the aisle? Was he doing that weird, sing-songy thing in a loud voice? Obviously, he was doing something conspicuous. Just wonder what it was.
Imagine the guy, sitting next to you, a mideastern type, young guy, maybe 30, eyes closed, hands on lap to either side with palm facing up.
He is muttering audibly, his lips are moving, and there is a bead of sweat at his temple. You can just make out him saying something like "Aloooo akhbahr" over and over again. You know enough to know that means "God is Great".
You look over, and you see the other passengers in the seats around you staring openly in your direction with clear terror in their eyes.
Yup. I would be nervous.