I think the issue here is that it is, of course, a single match, but played between two teams that have different statuses. And, quite honestly, football's governing bodies deserve all the associated nonsense that results from sanctioning such a hybrid, Frankenstein-esqe abomination as this...
They were making the point that Checkatrade Trophy matches are classed as first team matches (which they are for the lower league teams). Therefore, you can make an argument that all players for the academy U-21 teams that play in those matches have technically made their debuts in senior...
Well, to be fair:
Ben Hall out on loan (although currently injured)
Ben White (currently injured)
Warren O'Hora (presumably currently injured)
Josh Kerr is on the bench
He has certainly benefited from a couple of injuries in front of him, but he is keeping Josh Kerr out of the side.