I'm sorry but there's NO way he could "know" that he was infertile if he has never been tested. UGH, some people... Let me guess, he thinks he's infertile because thus far he hasn't gotten anyone pregnant?
Question for him: If he "knows" he's infertile, why bother pulling out? Hmmm? As that is a "method" to decrease the likelihood of pregnancy. (By the way, the pull-out method is really horrible because pre-cum has more than enough sperm to get you pregnant. So, unless you are absolutely sure he's not fertile, that has to be discontinued.)
I'd say take another test in a couple of weeks or so. If you are pregnant, now might be too soon to tell.