This is a feature in macOS, the “shared find clipboard” or something to that effect, that you apparently either love or hate, AFAICT from Googling and seeing people getting heated on the issue 
It is the feature that copies the text you write in a find input in application A to applications B, C, D, and so on. It cannot be disabled globally, AFAICT.
I often step through log files and data structures looking for occurrences of a search term, which can be a lengthy process. E.g. right now, I’m trying to fix bad data written to a bunch of MongoDB databases, by stepping through a huge JSON dump with an "id" : "" search term. Sublime is fantastic for this — even an application close and re-open will keep the current location I am at in the file.
However, one visit to Chrome and me searching a webpage for “compress”, and the instant I go back to Sublime, macOS synchronises that term to Sublime’s find input, and the location in the file is scrolled to the next occurrence of that word. Now I have to start over :’(
In Visual Studio Code, there’s an option called “Global Find ClipBoard”, which is disabled by default, that controls this behaviour, so that you can turn it off, so it is clearly possible to override this macOS feature. I would love to have a similar feature in Sublime. My input history is polluted with searches not made in Sublime, and trying to do work involving searching in two places simultaneously, such as iTerm and Sublime, means productivity death and depression
Thanks!