Why does it sometimes say 'Cohesion' within the user interface and the code?
DX8 used to be called Cohesion. When it was changed to DX8, some machine names that were core to the system couldn't be changed. It's also why many classes are prefixed with 'coh-'. Apart from making the naming within the code a little less consistent, it shouldn't cause you any problems.
DX8 has existed for many years before it was released as a product. It was previously called Cohesion. Now, this is the company name and DX8 is the product name for Drupal 8. For this reason, the name Cohesion occurs within the code and within Drupal's user interface.
Unfortunately we were not able to change all instances of the word Cohesion to DX8 without causing backwards compatibility problems for existing clients using DX8.
Apart from making the naming within the code a little less consistent, it shouldn't cause you any problems. All you need to do is be aware that when something is called Cohesion or includes 'coh-' it is to do with DX8.