Note that in Hebrew the adjectives גבוה/נמוך are both positional (high/low) and measurement attributes (tall/short).
So when I answered, "The tall bear eats the low turtle," that should've been correct?
Let't push that solution :) It may not be the best translation into English, but shows you understood the Hebrew, which is the point in my opinion.
In English - probably. In Hebrew - definitely, we typically think of a turtle as a more "horizontal thing" than "vertical", so we compare turtle sizes by גדול / קטן. I guess Hebrew's נמוך is even likely than English's "short", since "short" can measure horizontal length - say, from nose to tail - while נמוך can't. In the very unlikely case where one wants to stress the turtle's vertical dimension - the distance from the ground to the highest point of the shell? - I guess we'll use the words קמור / שטוח (in English: rounded vs. flat).
Having said that, you could stretch your imagination: in some children's book you can see personified turtles walking on their two hind legs (and talking, while at it). For these turtles it makes sense to use tall/short and their Hebrew counterparts.
Now since it works the same both in Hebrew and English, You can expect Duo to expect you to translate it quite literally.
The bear, chasing two turtles, finally found them up a tree. He decided to eat the one who was on a lower branch.