You have opened a Tube & Pipe fitting from the Content Center using the option “As Custom” and saved the file in a location of your machine.
Then, you have inserted the file you have saved in an assembly with the command Place Component, but the file is still behaving as a Tube & Pipe fitting.
For instance, if you right-click while inserting the component, you get the same context menu as if you were placing the fitting in a Tube & Pipe subassembly.
In the assembly browser the fitting icon is the same as if you have inserted the component directly from the Content Center.
The component cannot be demoted, etc.
This behavior is as designed, because the fitting still contains the authoring information that, for instance, would allow you to insert and connect it to a Tube & Pipe run.
So, if you want to insert the component as a normal part, after you open it from the Content Center using the option “As Custom”, you need to remove the authoring info stored in the part with the code you can find in the solution https://usa.autodesk.com/getdoc/id=TS13404549
After doing that, inserting the component in an assembly, you won’t get the Place Fitting context menu, the icon in the browser is the same as a normal part that, in case, can be also demoted, etc.
By the way, the fitting still has some Content Center properties as you can see from the context menu, right-clicking the component.
If you want to copy or mirror the fitting along with other assembly components and standard parts and the option “Reuse Standard Contents and Factory Parts”, this can be just reused or excluded.
So, if you want to remove any trace of the Content Center properties, you can use this Macro before inserting the fitting in your assemblies.
Of course, you can easily combine the two macros if you need to remove both authoring information and Content Center properties from the fitting before inserting it as normal part in your assemblies.