I think they made an error somewhere. The load was presumably 10 kilograms (22 lbs) of diamonds which equals about 50.000 carats. Now if it was cut diamonds then this should indeed be worth about 350 million EUR, however they were uncut, rough diamonds and thus far more less valuable then cut diamonds. However, since they are uncut, rough diamonds they are virtually untraceable and thus easy to sell.
At this point it is said that the value of the heist is estimated at 50 million (some say USD, others say EUR) which is still a very significant amount of money...