Maybe Trev had to technically fire Ellis because Ellis may have worked for the entire Athletic Department and not just the football team. I really don't know. Either way, here is how the conversation most likely went:
Trev: We have a nutrition guy, but he is a holdover from the last staff. We can let him go if you have your own guy who partners with the S&C coach.
Rhule: Yeah, I have my own guys I would like to bring in.
Trev: Ok, I will let our current guy go.
There are going to be a lot of changes going on in the next few months with the football team and potentially athletic department. I would recommend that you don't need to look for a deeper meaning with every move. Most of the time "it's just the way it is".