judging by that particular airline’s tags next to his press credentials, he obviously flies mostly domestic for his job and they do not nitpick over carry-on size if it’s just one and fits in the overhead space which that one clearly does. If he flies one of their little connection carriers, it could be a problem but I imagine it could be crammed up there also.
OTOH you can bottom of the stairs “gate” (No gates at the airports I fily into and out of) check a bag that won’t fit in a puddle jumper and it’s first off the plane and you pick it up at the bottom of the steps as you are deplaning. Because by the time they wheel the stairs there, shut off all the stuff they don’t want idiot passengers to walk into etc., the baggage folk have already got the baggage at the end of the stairs for you to pick up and go.
You must not ever travel on very small planes. You can barely carry a purse on some of them. The ones that fly out of our normal airport have 3 seats across. I can get my Tom Bihn bag under one but I have my feet on it. There is no way I can carry even the smallest carry-on bag into the plane. They are far more like small private jets with self loading cargo than normal passenger planes. There is only 1 side with an above seat storage place.
This is the most comon aircraft at the local commercial airports.