"Eso no es tuyo."
Translation:That isn't yours.
According to this reference, eso means it is a little farther away than near (este), but still in your general vicinity. Aquella is NOT in your general vicinity. http://www.spanish411.net/Spanish-Demonstrative-Adjectives-Pronouns.asp
It should be accepted. Did you report it when doing the exercise? DL doesn't make changes based on comments in this forum.