I’d be surprised if they want people with overall very poor stress responses; that’s a liability in jobs where the risks and stakes are considerably lower; and having people wash out before you’ve gotten that you want from them isn’t free.
The target is people who are concerned specifically about their future outcomes in the context of imminent exam results and/or handling that follows that. That’s an obvious target for “unlike what you see as every other option, we won’t hold the grade you expect to get against you…” messages.
It looks especially shabby given that the UK still recruits under-18s; but the plan is otherwise identical to the usual ‘economic conscription’ mechanisms that encourage enlistment among people (and often from specific areas) where the army is among the few state-backed vocational options remaining.