I live in Northern California. My roof is 8 years old and was intalled by a licensed contractor and has never leaked. However, a roof inspector says my roof is not up to current building standards that would require the use of ridgecap shingles. Apparently the contractor that installed my roof used a different technique on the ridgeline. I can see that the ridgecap shingles are what is recommended but are they the only approach that is certified by a roof inspector.
I agree with Jim Stewart and Ecnerwal that it’s highly unusual that a Building Inspector would require you to change anything, unless you are doing a re-roofing project.
If you want to argue with him, I’d ask him to review Appendix J of the Code for existing construction, especially if it’s not leaking.
Here is GAF Roofing’s installation instructions for typical ridge cap installation. Each manufacturer will have slightly different installation instructions, but will all be similar.
If you have a ridge vent, here is a site for that:
Perhaps, what the inspector saw was a modified ridge cap made from regular shingles, (which is often done,) but he may not be familiar with that technique.