They are purposeful, I don't think Pemulis ever gets one thing right in the novel. His explanation of Annular Fusion is a good example, unless you also want to make the case that Wallace got the made up science wrong as well. Pemulis grew up in a place where he was generally the smartest person around and was able to bluff his way through life without much effort. Then he got a scholarship to somewhere with actual expectations and standards but Pemulis kept on with his lazy ways. Pemulis is probably smart but his laziness and arrogance keep him from ever achieving his own intelligence, he is forever lobbing but is a bit too slow to get to the net in time.

Vast majority of character's are well explained and the answers are all in the novel, just need to look at their childhood and upbringing.