There are really two critical paths. There is the critical path to the project (which is the latest date in the schedule) and there is a critical path to any task in the schedule.
When we display the critical path using the Inspector, we are displaying the critical path to the selected milestone (with a target date). This displays all the tasks that are driving (the critical path to) that milestone. Some of those tasks could be on the critical path of the project, some may not be. To differentiate these in the schedule:
Tasks that are on the critical path of the project will be displayed with red text and their Gantt bars will be red
Tasks that are NOT on the critical path of the project (but are critical path to an Inspector-selected target or task) will be displayed with black text and their Gantt bars will be red with a black line underneath, indicating that they are on the critical path to that milestone, but not on the critical path of the project (i.e. the project critical path)
Below is a little simple example that makes it very clear. The first (project) critical path is red (no black underline). This is the true long path to the end of the project.
Notice with the full schedule showing, the project critical path is in red and the second path is blue, because the second path has 10 days of float. There is only one critical path (e.g. 1st: critical path).
We can isolate the project critical path using the Inspector, below. This is the long pole or longest contiguous path in the overall project. The symbol is RED with red connector lines.
Next we use the Inspector to find the critical path to “2nd: end” - this is the second path that has 10 days of float.
Notice that the second path turned red, yet this time it has a black line under each red bar and the connectors are black lines. This is to indicate that this is not the “real” or longest "project" critical path, but rather the critical path to the selected target (identified in the Inspector), which happens not to be on the project critical path, hence the black line under the red bar.
This feature enables you to view a critical path to any target or task in the schedule. It is a "bending" of the term "critical path," but it simulates the process of finding the longest path to any task/target/milestone in the network. Once selected, you can then Peel-Back the layers of critical path from the selected task/target/milestone, regardless of it being on the real project critical path.