Kali has a Night Vision Sniper Scope law that say the scope must meet 3 criterias. Night Vision, reticle and IR Illumination. So in essence unless the thermal has some sort of IR lum (which is moot) a thermal scope does not meet the California PC as a NV Sniper Scope.
To further elaborate on the silliness of the law, a PVS-14 weapon mounted behind a MRDS or day scope automatically becomes a NV Sniper Scope due to it's internal 6-8ft IR LED illuminator.
The only case law we've found was from the 80's when a hunter was arrested for a dedicated NV Scope but was thrown out due to the scope not meeting one of the criteria points, and that was the lack of any IR Illumination.
Bottom line, a thermal scope on its own is legal in the state of Kalifornia. Hope this helps.