No that's definitely a mistake in the article. Not only are the RER tunnels from the 70s, they also run much deeper than the metro tunnels. They didn't exist in any form at the time. The metro tunnels did, though
The northern terminus of the Ligne de Sceaux opened at Luxembourg in 1895. Between 1973 and 1977 it was converted into RER B.
( https://en.m.wikipedia.org/wiki/Luxembourg_station_(Paris) )
I know in NYC that water pipes and electric tend to get routed through/around subway tunnels once constructed.