The response times provided in the article are for the whole process of searching and returning the entity. The indexes themself are obviously a lot faster - to be precice we are using DynamoDB for storing the indexes, which most times return results in <10ms. Compared to other databases this may still sound slow, but we know that we won't run into scaling issues in this way and that's kind of what matters currently most for us.
Hope that somehow makes sense what I wrote.