I remember this being a problem on an older phone, and I found an option for voice searches where I could limit where it searched. For example, I could turn off web searching, location based searching, calender searching, etc, and only do a search in my contacts.
I don’t know if that setting was device specific, but I’ve started having the issue again on my LG V60. I’ll say something like, "Call *city name* water treatment" for my contact listed as such, being a municipal water treatment plant. Instead, it’ll try to call the local Culligan dealer or whatever happens to be the top result of a generic Google web search. I’ve tried to find that setting again, but with no luck. Anyone know if it still exists, or where to find it?