I have never once heard it was CGI. The theory was that it was faked and filmed in a closed set by Stanley Kubrick. What would you possibly CGI anyways, the buggy driving around in the dirt or people on strings being pulled up in the air when they jump? All of those would be better done with practical effects even today.
For what it's worth, I believe that we landed on the moon AND that the video was likely faked. They video just doesn't hold up when viewed on modern equipment instead of on a 20" 1970s tv via OTA broadcast. Not to mention a lot of video is "missing" with the excuse that they overwrote the tapes, you know because NASA didn't have the budget to save their tapes and had to reuse them.