LINQ provides a new way of seeing an Information Ecosystem.  It doesn't replace existing tools such as Business Process Mapping and Enterprise Architect tools; it augments them by creating an accessible framework that allows non-technical executives to better understand.

LINQ is focused on the flow of information through the organisation; the Information Supply Chains that connect sources of information to outputs.  LINQ models all the information, actions, people and systems to achieve that.

BPM is focused on the visual depiction of joined-up tasks or actions that constitute a process.  BPM is focused on outcomes, the actions, tasks and procedures to achieve them and the person or people performing those tasks.

One of the challenges for Business Analysts starting out with LINQ is learning to 'Think like LINQ' in order to capture the Information Supply Chains rather than the Business Process Map.  

There are other articles tagged 'Business Process Mapping' which address some of the specific differences.