No way that is true. You're right on the population it was 4.3 billion, but consider that a tiny percentage of people in populated countries like China, India, Indonesia, and Brazil had access to a tv at that time. Even if every single person in the U.S and Europe watched it you wouldn't have those numbers. I'm sure a lot of people watched it but that's a hype job. I'll believe that number when I believe that 80 million people voted for the crypt keeper.
Modern statistics of households with tvs which would have exponentially grown since the 70's
https://www.statista.com/statistics/268695/number-of-tv-households-worldwide/