On the contrary, I think they are saying they want the guitar to contribute in a way which is appropriate to the tune - which equally applies to other instruments, of course.

One of the joys of sessions is the opportunities they offer for improvisational experimentation, and when a skilful player tries something off the wall which works (such as that blues chug), the results can be magic. Unfortunately, the guitar is one of those instruments which is easy to play but difficult to master. There are plenty of unskilled or inexperienced guitarists who are unable to identify the rhythm or the key. The negative impact they can have is often greater than that of someone on a melody instrument who is unsure of the tune.