You doesn't understand the point that when u are solving this problem prefix and letters are two different part in the process.
When you read substring sorted by len + ascending lexicographic order, ur brain think automatically this is for the second part of the string, the letters, like "aaa" in your example.

At the end the two description mean the same but one is much more clearer and faster to understand, there is already a 40 upvoted comment 5 years ago from helloRupa wich had rewritten all the description of this kata.

And fun fact by watching all the comment I have seen the same answer of you 4 years ago to the same type of comment.

Just looking at the comment everyone is complaining at the sorting thing, it should be said more clearly like:

1.Length

2.Prefix of string i.e 1, 2, =

3.Lexicographic



Everyone is missing the same second step, understanding the description should not be the hardest part of the problem but it's clearly the case here.

Thanks!

So smart ! :O