What is the basis for the term "psycho-epistemology"?

I wouldn't say psycho-epistemology is not concerned with knowledge at all. It's concerned with the way one thinks, which is the means by which one reached knowledge. The purpose of epistemology is to provide guidance to our conscious thinking processes—the part of our thinking that is under our direct control. The purpose of psycho-epistemology is to understand the role of our subconscious—our psychology—in that process.

Moreover, part of what psycho-epistemology studies is, in effect, the epistemology that one has automatized in one's psychology—one's thinking habits, one's automatized ways of processing information. Accepting a given epistemological theory (whether Objectivist, rationalist, or empiricist) and automatizing the practical advice derived from that theory results in a distinctive set of thinking habits. It is in this sense that we can say someone is, e.g., a rationalist, even if he doesn't consciously accept, or has never even heard of, rationalist epistemology—because he thinks like one, in practice.

All that said—it's not necessarily the greatest term. For one thing, it's kind of long. But it makes sense and it's what we have, so we use it.

There is an extensive collection of excerpts on "Psycho-Epistemology" in The Ayn Rand Lexicon. The second excerpt, in particular (by Leonard Peikoff), seems to answer this question.

"“Psycho-epistemology,” a term coined by Ayn Rand, pertains not to the content of a man’s ideas, but to his method of awareness, i.e., the method by which his mind habitually deals with its content."--Peikoff. The link can be accessed here: http://aynrandlexicon.com/lexicon/psycho-epistemology.html

I guess that answers :)