Okay, well, my viewpoint is:
the reason why one could argue that Socrates was a "common" sophist (being payed for knowledge) is, because he also got payed for his knowledge, more often with (personal) favours than with monay, but he was payed. so far the conventional Sophist.
deeper:
sophist as in altering his knowledge as to suit what people expect, or being payed for.
well, when conquering people with questions that lead to further questions, it is inevitable to keep on questioning and not agreeing on something eventually. so here it is probable that he contradicted his own viewpoint just to prove that another person did not have an answer to this question.
secondly, in "Apology" (thats how the text was called that we had in our lecture) he says he will not bring his family into the courtroom, but he mentioned it and that alone already contradicts his "not using his family to gain extra points".
that, for now, is the only (possible) explenation i could give :)
Greetings