The grape smell you got from the one may be the typical smell they most all have. Try some other and see.

I have recently aquired "Visions Pink." It has come into blom and it is indeed fragrant.
I reccomend it. It is a small plant with a tight clustered bloom.
To my nose though it has a typically yeasty fragrance, like the flowers of bayberry or holly.
I would love to find a grape scented Astilbe though!
Was the plant you smelled, redolent of grapes (the fruit) or grape must perhaps?

Sincerely,
Matt Di Clemente