I am conducting research on a potential client to determine if they are a good fit for me. The client has recently submitted a disavow file which blocks 400 domains and around 2,000 URLs. A significant number of the URLs they've blocked belong to the client's own website and contain parameters that lead to a single adult site at the end of the URL.
Example: clientsite.com/?URL=siteinquestion.com/result/type%of%adult
All of these URLs 301 redirect to the clients root domain. When going directly to the parameter URL it leads to what you would think, however, there are no backlinks to the client's site when reviewing the source code. Additionally, in Ahrefs the domain in question is not present in the client's backlink profile.
What do you think happened? Were they hacked? Also, I don't see a point of adding these URLs to a disavow file. Would you agree?