Hmmm. I wonder if there is any research to back that one up. It is an interesting hypothesis, but evolutionarily speaking, language is a more recent development than information acquisition via visual methods, when one stops to consider it.
Social, yes; though that means quite different things to different individuals, as any extreme extravert/introvert could explain.
I mean, anecdotally, it matches what I (and other teachers) have observed to be true; that it is hard to pay attention to anything which is non-interactive for very long, and that students-- in general-- have a hard time paying enough attention to more than a few minutes of video instruction. Research has shown that to be true, too, so it's more than just anecdote and instinct operating. (I posted several of those studies earlier in the thread.)
Oral communication is a different medium entirely, even if it is a lecture setting. It's an intriguing idea. I agree that it's social in a way, but I'm not sure that I agree with formal, quiet, and real-time being the "best" learning environment, if only because none of those is exactly nonsubjective terminology.
I think it probably has something to do with intrinsic motivation and how learning style preferences play into that student motivation. More young students are socially motivated than not, but learning shifts gradually away from that primary mode as students mature, too. College faculty in particular are in a position to watch autodidactism develop in real-time-- most students have to learn the supporting skills (executive, discriminating) to leverage it well, even if they have natural inclinations that direction.
