does 'I introduce someone as something' mean 'I introduce someone as I am something' or 'I introduce someone as he is something'?
Idiomatically, the as would usually refer to the person being introduced, and to note that you are something, you'd be expected to use different phrasing:
As the captain of FC Smalltown, I introduce John Smith, our new striker.
But there are cases where the as would refer to you, the introducer:
Tomorrow, I'm going to introduce John as his manager.
So in the grammar sense, it can be ambiguous - but unless the context makes it very clear that the as-part refers to yourself, it'll probably be understood to refer to the introducee.