Chances are it was already in flower stage when clone was taken.
Just found a flowering top/soon to be clone of mine own, was shocked to see it flowering then remembered its momma died a horrid 2x4 death the 1st week under 12/12.
when removing this plant from your grow area I would suggest you slide a plastic bag over it and seal it with duct tape before you bounce it around and send pollen everywhere contaminating your grow area. My guess is you have already taken her out, but for future that would be a wise way to do it.
keep in mind too that clones are not new plants... they are parts of very old plants, just being forced to root in a new place. I used to have a white widow mother that was almost 3 years old. Every one of her clones would start to show pistils before they were even out of the solo cup stage and still had a month to go in my veg tent. That didnt mean they went into flower though, my lights prevented that.