It is acting suspicious and as you stated is done because counting down from 10 on an aeroplane in today's climate in any language is potentially going to unsettle. Why? Who the fuck counts down from 10 let alone any number on a plane? Counting down tends to trigger association in anyone's head with something happening at 0. Especially if you are audibly counting down to get the attention of those around you. It doesn't necessarily need to go to instantly being chucked off, but being questioned what the hell you are doing?
As I said, plane etiquette, get on plane, sit down, listen to music/watch shit, eat, take a dump (pls don't), sleep, get off plane at destination. Success. No one bothered you, and you didn't bother anyone else. Anyone wanting to veer outside standard decency when we're all crammed into a metal flying tube and I'm going to question what your agenda is and/or why are you being a nuisance? The biggest nuisance I expect on a plane is children kicking seats, which I'll tell their parents about, drunk people, who can be ejected and other normal human annoyances. Not asshats counting down to try and get a reaction or any other shit for their reactionary YT page.