It would seem you are expecting a planar straight line to automatically be associated with a diameter dimension.
Sketch entities created in drawing mode are not equivalent to sketcher geometry in part mode. They are "dumb" and not driven by the model geometry and should be avoided.
I would strongly suggest that if you are using Creo Parametric as a design tool, in general your 3D model should drive what is on the 2D print and that you not deviate from this paradigm without a compelling reason to do so.
I can see in the tree that you are creating draft entities; can you explain why you are adding these in the drawing? If it is to get dimensions in the drawing, then it is almost certainly not best practice to do so.
Assumptions:
You sketched the orange line in drawing mode: it will get a linear dimension as you have seen. This is expected from any 2D drafting software I have ever used including Creo.
If you have a hole in the 3D model you should be able to show the feature dimensions in a drawing. If you dimensioned the diameter when creating the hole in the model, then it will appear as a diameter in the drawing when shown.
In your image above the 26 diameter is in (), this could indicate that it is a reference dimension in the model. You should investigate that and understand why it is that way in the model.
To show dimensions when in drawing mode: Annotation tab-> Show Annotations and select dimensions
Here is a sample model and 2D drawing with annotations from the model shown on the drawing. Note the model annotations in the drawing tree. All dimensions seen below are in the model and displayed in the drawing.
