Yeah, I don't know if it's true either. On the surface it makes sense to me, in that if you do pay your balance in full before a statement cuts, the statement is 0. But like
@Judique says, you did both spend and make a payment. That module did say where this really hurts is new credit users, who are trying to establish a credit history.
I'm in the same boat in that we have zero installment payments, no car loans, no mortgage, etc. So I think we probably take a hit for that as far as credit mix goes and our scores aren't quite as high as some others, more in the high 700s. But we've always been approved and most commonly, instantly, so not sure we could get much more of a benefit from a higher score.