Notice how the narrator takes 2 1/2 minutes to tell you what to think, then plays the clip for you? This is to give you the idea that you are thinking for yourself, but you aren't, he's already told you what to think.
It's 1928 and the person is an "extra" with the only job of walking across the screen to illustrate activity. He is hiding his face for one or two reasons:
1) He's a guy in drag and the idea is to convince you that he is a lady.
2) He's talking to someone off camera and is trying to hide that fact.
Had you watched this clip in 1930, you would have come to the same two conclusions. But since you live today, you see it thru today's eyes and experiences: "It sure looks like he or she is talking on a cell phone. "
This is what James Burke was getting at in the opening of "The Day the Universe Changed" when he said that "what you see, is what your knowledge TELLS you, you are seeing... when your knowledge changes, (what you see) changes".
This is also why people long ago thought that the sun went around the earth - because their life experiences and biblical interpretation set them up to think that. NOT because they were stupid or illogical. They just knew different (and less) stuff than we do!
This is also why eyewitness testimony can mess us up. Case in point, take eyewitness testimony of a plane crash where the crash was also caught on video. The testimony will often contradict what the video SHOWS, because, again, we "see" not only with our eyes, but with our knowledge and life experiences.