OPK as HPT?

Jessica • Mommy to two precious little girls. TTC #3 and hoping for a boy this time!
I had a positive digital opk at the end if my cycle when pregnant with my second baby, and that's when I decided to run out and get an hpt.  A few months ago the same thing happened (positive digital opk), except all I got on the hpt was negative.  Wondering if I had a blighted ovum that time, or if it was just a fluke?  Has anyone else done this?