Your textbook probably just simplifies some facts. Russian front against Germany completely collapsed in early 1918. Estonia declared independence on 23rd of February as Russian troops retreated from Estonia and German troops had yet to occupy it (they would occupy it a day or two later). The situation was similar in Lithuania, where in the face of collapsing Russia, Lithuania declared independence (but was also occupied by Germany).

In March of 1918, Russia and Germany signed the Treaty of Brest-Litovsk (this is what your textbook means when it says "Germany had taken these states from Russia in 1918"), where Russia gave up large swathes of its western territories to Germany.

However Germany lost the war in the west and surrendered on 11th of November 1918. This meant that German troops were pulled from the east and the Baltic states established their own independent nationalist governments. Latvia declared independence, as they had not done so in February/March.

Thus Germany had in practice already given up their Eastern conquests by November 1918, but only in the Treaty of Versailles were the new borders of Germany officially agreed upon.