I'm pretty sure he did realise, I think he mentioned something about her attempts to find 'volunteer work' later on.
However, he did sound a little as you suggest, i.e. he felt she would be top volunteer in no time, and popular with the customers as well.
Ah, OK, then - I agree he's probably playing the long-game, though. It's amazing how many people assume that substantial remuneration is automatically always there to reward (what they perceive as) brilliance - even in a charity shop; almost like you'll be (before long) paying her purely for being brilliant rather than for fulfilling a role that is required, budgeted for and for which she is genuinely the best person!
My only other concern, with her being so 'brilliant' yet somehow not being able to contact you herself, is that he might be controlling her in some way. Possibly quite a reach, but this could be his way of trying to shoe her in for a job and then turning the pressure on to her to translate her experience into being paid to 'earn her keep' and/or to show her who's boss (i.e. the one who really earns the money) 
The fact that she hasn't contacted you herself could equally signify that she is too shy or lacking in confidence to make that initial reach OR that she doesn't want (or even have any knowledge of) the job that she could end up doing. As you will very well know, having a volunteer who doesn't truly want to be there volunteering is much worse than having no volunteer at all.