As a lonnnnnng time ATCO, I see two sides to this.
1. The controller should have announced the fact that the kid was going to do a bit of RT, so that the Captains knew what was happening. [Did that bit get missed?]. Is that suitable for a major airport? NO!!
2. It's a dumb thing to do anyway. Period. Who knows what scenario is going to arise in an instant? I know you can instant switch the headset, but that's not the point. At a lightly-loaded airport, perhaps - with pre-briefing of the flight crews.
Sorry for the guy who is going to lose his job. Nice
PR, bad skills. Sorry, not much sympathy here. I don't think I would have let that happen in
my Tower.