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.
גבוה and נמוך .both are vertical [[Ehm. How do you write a bilingual sentence? My editor mixes directions]] A turtle is horizontal to me, and short tells me something about its length, not its height.
Using the words high and low for altitudes is the more common way in my language anyway.