As I looked through the story, I didn’t see a reference to why they think this is true. Is there a video? They didn’t even bother to quote an unnamed source this time.
The source is the Prigozhin’s VK page. (russian facebook clone)
I don’t speak russian, but based on your previous posts I assume you do so you can translate:
https://vk.com/concordgroup_official?w=wall-177427428_2145