That sounds, well, bizarre.
I've lived in San Diego for 45 years, just a few miles from Lemon Grove, and I have been openly carrying a fixed-blade here for about ten years now without any problem. And many cops have seen me do it.
In fact, I was at Home Depot in Lemon Grove (on Broadway), there was a cop car parked in front of the store, and I parked my motorcycle right next to it. A cop who was sitting in the car saw that my open jacket had momentarily covered my knife thereby making it concealed, which is illegal. He just gave me a very friendly heads-up about it, I adjusted my jacket, thanked him, and then we went our separate ways. He never drew his pistol, neither did his partner, nor did he ask my name or ask for my ID.
On another occasion I walked into a fast-food place in La mesa (right next to Lemon Grove), I walked right past a table of five or six cops sitting at a table eating. My knife was in plain view to them, they were close enough to reach over and touch it. But not one of them said a word to me. And I was fresh off my motorcycle and covered in leather.
Here's a pic of what they saw (except I was wearing leather pants as it was cold out)-
Several other cops have seen me and my knife in San Diego. We've passed each other at 7-11, and I've been stopped at stop lights right next to them. And they have never said a word.
I know several other people (mostly bikers) in San Diego who openly carry fixed-blades and have done so for many years without any problem with the cops.
I also have a criminal defense attorney who has lived and worked in San Diego for several decades, and he has never heard of the cops giving people any trouble for openly (and legally) carrying a fixed-blade.
Like I said, I find your story bizarre. Because it goes against everything I have ever experienced here in San Diego, and everything I have ever heard from people I know. And California state law (penal code 20200) specifically defines an openly carried fixed-blade, in a sheath, carried on ones belt, as legal.