Here's the essay I wrote for the second task published by ETS at https://www.ets.org/toefl/ibt-
There is a first paragraph that isn't shown in the text box. This one also got 5.0.
Actually, this is the second essay that I wrote for this task. The first one was only 104 words, and got 4.0 despite being grammatically perfect. This suggests that ETS is weighting the length of the essay.