I was actually just trying to find a fitting community to ask, but couldn’t find anything fitting. Was this just a simple editorial error, or is there something making the statement technically (virtually?) true?

UPDATE: Apparently, I was superficial enough to not take a closer look at the 1973 title. I never even heard of it (I don’t think it was on TV in my country), and I didn’t even consider the responsibility of it not being a standalone film. Thanks for solving the mystery, folks!