Translation:You have accomplished much in very little time.
It seems that Spanish "realizar" only refers to implementing actions in the external world, and cannot convey the sense of coming to an understanding of reality which English "to realize" can mean. Or in other words, the Spanish "realizar" is clearer in its meaning than the English "realize" is (the English is ambiguous).
So, perhaps Duo is marking as incorrect the literal translation of "realizar" as "realize" to let us know that "to realize - realizar" is a tricky equivalence. This may be especially important to keep in mind if the English "to realize" is more frequently used in the internal/mental sense than in the accomplishing real-world actions sense--especially since Spanish has a different verb construction for the internal/mental sense i.e. "darse cuenta."
Yes, they can mean the same thing. However, "You have realized much in very little time," sounds awkward to my (American English) ear--it sounds like "you" could have solved a mystery quickly. Of the various translation choices, "accomplish" seems to be the best fit for the given sentence. The two mean the same in constructions like, "His dream to climb to the summit of Mt. Everest was realized." Substitute accomplished for realized and the meaning of the sentence doesn't change. I hope this helps.