They didn't claim that current space standards are at a peak, and further improvements in technology have already been hinted at providing optical storage sizes in the hundreds of gigabytes and beyond. Nor did they claim optical storage will be disappearing anytime soon. After all, CDs are still around.
Sony didn't speculate on what sort of new technologies will succeed optical formats. When the day comes portable 50TB media is in demand, however, Sony believes it won't be an optical disc that provides it.