Here is the first part of the original recording:
Yep, that surely sounds like Steve Reich. As he says in the interview, without that pulse it is a very different piece.
Another thing I learned from the Reich interview was the importance of the influence of John Coltrane, especially this piece, which is nearly seventeen minutes on an E chord:
In the interview he talks about the increasing tension that comes from the fact that the longer the music sits on the same chord, the more the tension of the expectation that the harmony will change. Of course, I suspect this is a whole lot less true these days as everyone from John Luther Adams to Nico Muhly is doing drones, drones, drones.
But it seems clear that the guy we need to credit with the return of the pulse to music is Steve Reich. Unless perhaps Philip Glass was doing the pulse back in 1964? It seems not, as from 1964 to 1966 he was in Paris studying with Nadia Boulanger, who had a fairly traditional approach to composition.
This sort of thing, claims as to who was the first to return the pulse (and harmony) to music or who was the first to do cubism in painting (Pablo Picasso with his Les Demoiselles d'Avignon of 1907 apparently, just edging out Georges Braque's Houses at L'Estaque of 1908) seems odd to me, but obviously of great importance to the artists involved. My feeling is more "who was it who really developed the idea?" It was certainly Steve Reich as Terry Riley seems to have done nothing else of any significance since "In C".
It is interesting to contemplate how Steve Reich was able to take the simplest of musical ideas, repeated eighth-note octave Cs, and use that as a foundation to reinvent music. But that seems to have been what happened. The path leads directly from there to this: