I don't understand what you mean but if the infinite scroll content has already been loaded, the HTML for the same will update in the element inspector as well and you can search for the string there. Of course it's hacky but I use this technique all the time.
Ok I was assuming they meant that if they did control + F on the webpage and the string was towards the bottom area, the page would start infinite scrolling automatically after locating that string via search(and they wanted to avoid this). Heres a similar example, if I wanted to get the contact page link(located on the footer) on an infinite scroll page, I would never be able to get to the bottom because of infinite scrolling. But I could do a Ctrl +f on the inspector to locate the "contact" string and copy the contact page link from there.