Hi doodyhead/maryellen!
Yes, Pink Floyd certainly was a blues - or rather R'n'B - band in their early years, before they recorded "The Piper At The Gates Of Dawn".
I don't know what soundtrack you're referring to, but I have early bootleg recordings of them doing "I'm A King Bee" and Syd's own "Lucy Leave" (1965), which could easily have been done by the Rolling Stones.
I think the statement about the British blues bands was after they started doing their more phsycedelic freakout shows with long improvisations. That would have been around 1967, just as the so-called Blues Boom started.
Thanks for the note about David Gilmour!
I didn't know he was a Greeny fan!