Yes its all a bit confusing isn't it? This is what the mighty DWP itself says:
'Case Managers are trained DWP staff who are familiar with the legislation governing PIP, but who do not have a healthcare background. The HP enables Case Managers to make fair and accurate decisions by providing impartial, objective and justified advice.1 Jan 2016 assets.publishing.service.gov.uk › ... PIP assessment guide'
The second sentence about making 'fair and accurate decisions' etc is likely to evoke a somewhat hollow laugh in many claimants!
Sorry, but the link I gave in my last post does not seem to work - or doesn't when I click it using my mobile anyway! If it doesn't work for you too you can find it by doing a Google search on 'what does a DWP case manager do?' On the list that comes up you will see 'what does a PIP case manager do?' or similar wording. If you click on the downward arrow it will take you to the quote in my last post which includes the link, if you click the link this will allow you to download the DWP PIP assessment guide which presumably contains the quote about PIP case managers. Hope this helps.