Who is Maconie and what is his program? If it is Stuart Maconie, then I will take the information with a grain of salt, but still interested in where he got it.
Robin Maconie, a NZ musicologist famed for his detailed coverage of Stockhausen in his
The Works of Stockhausen from the early 1970s--a book I heartily recommend, more recently republished as
Other planets and revised to include updates through
Licht.
I think James has read too much into Maconie's words in the summary for the radio broadcast. There is a fleeting reference to
Gruppen in the literature when Maconie establishes the parallel between Stockhausen and Carter as two composers that were interested in simultaneous use of different tempi in music. However, Carter's use of it predates Stockhausen's, as evidenced by his
String Quartet of 1951 and an article about rhythm from 1955. If anything, the influence would have been the other way around.