Impossible to say based on that description, but it certainly could be.
If light is hitting the plants during their dark time, its a light leak. If not, it isn't.
Note that your room doesn't have to be absolutely pitch black during flowering.
Flowering plants can handle a small amount of natural ambient light without stressing.. . .but you don't want the equivalent of even normal room light for one second, let alone sunlight or grow-intensity light. Put it this way, if you can see easily in your grow area during the dark period, you have TOO MUCH LIGHT!