Here is a possible bug in testimonials.
As per instructions I have created a category testimonials and applied it to some posts. But in the testimonials on the home page, even posts without category appear as testimonials.
When we tested the theme locally, we were unable to find such issue. The testimonial section will only display those post that is associated with the particular category which is chosen to display in Testimonial section.
So please can you post your site URL so that we can inspect the issues further and help you.