If it was extract, it was probably because you didn't mix your top-up water thoroughly enough. That happened to me on my first batch, and may around here cite that as a cause of low gravity readings.
Come to think of it...I may have taken the reading right after topping it off but before I mixed it...maybe the OG was higher than anticipated...thanks gents
That's the most likely answer. I pour my chilled wort through a fine mesh strainer on top of the FV. Dito with top off water. Then stir with my paddle for 5 min solid like a scene from psycho.
lolz Yeah,I keep thinkin of the shower bath scene. Ree ree ree ree! (the violin thing with each stab). Put the jokers laugh on top of that..."yah wanna know how I got these beers"?