Help Settle an Argument - Should an Ex be Confronted About a Huge - and Terrible - Lie?

My coworker - and good friend - and I were having a discussion about whether or not he should confront an ex or not. A little back story - a few weeks ago they hooked up quite a few times using no protection. As for her, after her second child she had her tubes tied and has been like that for 5 years now.

She is now in a relationship with a guy who can't have kids. However, a couple of days ago she called my friend and told him she missed a period and was late. As in late late. Naturally, this freaked my friend out because this would make for a nightmarish situation.

Now, yesterday they are talking on the phone and of course she is having trouble with this guy and turns to my friend. There is a small, insignificant argument which ends quickly. He point blank asked her if she really was late to which she said yes. Not more than 10 minutes later she calls him back and said "I just went to the bathroom and my period came so you can now rest easy."

I told him that was a lie. Either she lied from the beginning for reasons known only to her or she lied at the end. But my gut is telling me he is being lied to. So, what should be do?

To lie is one thing, but to lie about possibly being pregnant is a whole different ball game. And a pretty low one at that.