they are correct, it is blossem end rot, first things first. go over your plants thouroughly and remove all fruits that show any symptoms. Calcium is required in relatively large concentrations for normal cell growth. When a rapidly growing fruit is deprived of calcium, the tissues break down, leaving the characteristic lesion at the blossom end. Blossom-end rot develops when the fruit's demand for calcium exceeds the supply in the soil. This may result from low calcium levels in the soil, drought stress, excessive soil moisture, and/or fluctuations due to rain or overwatering . These conditions reduce the uptake and movement of calcium into the plant... or rapid vegetative growth due to excessive nitrogen fertilization can also factor in.